Selenium nanomaterials and methods of making and using same

ABSTRACT

Method of preparing a selenium nanomaterial and selenium nanomaterial articles. The method may include forming a saccharide coating on a surface of a solid support material, treating the solid support material having the saccharide coating on the surface with a selenous acid solution, and heating the solid support material to form the selenium nanomaterial on the surface of the solid porous support material. The saccharide may include a monosaccharide, a disaccharide, or a polysaccharide, or a combination thereof, such as sucrose, or fructose, or a combination thereof.

CONTINUING APPLICATION DATA

This application claims the benefit of U.S. Provisional Application Ser.No. 62/240,764, filed Oct. 13, 2015, which is incorporated by referenceherein.

BACKGROUND

In recent years, selenium nanoparticles (SeNP) or nanospheres (SeNS)have gained increasing attention due to their versatile biologicalactivity and lower toxicity as compared to other forms of selenium.Since selenium is a good photoconducting material, SeNS have beenintegrated in high-power batteries, solar cells, and electronics. Onefocus of SeNS applications has been their biological activity includingantimicrobial properties (e.g., the prevention of biofilm formation),antioxidant abilities, and anti-inflammatory effects. SeNS can increasethe susceptibility of cancer cells to drugs, thereby acting as a goodanti-tumoral and a chemopreventive agent. SeNS are also used in avariety of chemical and analytical processes including controllingcrystal growth, sensing, biocatalysis, and cellular imaging applicationsdue to their intrinsic fluorescence and enzyme-like properties.

Due to their high adsorption capacity and strong affinity for heavymetals and other toxic elements such as zinc, cadmium, and mercury, SeNSare also used in water remediation. An urgent need for cost-effectivemercury removal technologies is clearly justified by the major threatthat mercury causes not only to aquatic life, but also to human healthby entering the food chain. Mercury contamination of lake waters resultsin mercury accumulation in fish. A number of technologies have beendeveloped to remove mercury from water. However, many of thesetechnologies have costs that hamper their operation on a large scale,and some of the materials used in these technologies may themselvesresult in a health risk if leaked into the environment.

The need remains for practical and efficient technologies for removingmercury from air and water.

SUMMARY

The present disclosure provides selenium nanomaterials, including, insome embodiments, selenium nanomaterials bound to a substrate; methodsof preparing selenium nanomaterials; and methods of using seleniumnanomaterials.

Various embodiments include methods of preparing selenium nanomaterials.In some embodiments, the method includes forming a saccharide coating ona surface of a solid support material, treating the solid supportmaterial having the saccharide coating on the surface with a selenousacid solution, and heating the solid support material to form theselenium nanomaterial on the surface of the solid porous supportmaterial. The saccharide may include a monosaccharide, a disaccharide,or a polysaccharide, or a combination thereof. In some embodiments, thesaccharide may be sucrose, or fructose, or a combination thereof. Insome embodiments, the saccharide contains fructose. In some embodiments,the saccharide includes fructose, sucrose, lactulose or turanose. Thesaccharide coating may be a homogeneous saccharide coating.

In some embodiments, the step of forming a saccharide coating on asurface of a solid support material includes soaking the solid supportmaterial in a saccharide solution. In some embodiments, the methodfurther includes removing excess saccharide solution from the materialafter soaking the solid support material in the saccharide solution. Thestep of heating the solid support material may include heating at atemperature in a range of 110° C. to 120° C. In some embodiments, themethod further includes quenching or washing the solid support materialhaving selenium nanomaterial on the surface.

The selenium nanomaterial made by various methods may include seleniumnanomaterial on the surface of the solid support material having anaverage size of 50 nm to 150 nm.

In various other embodiments, the method of preparing a seleniumnanomaterial includes soaking a solid support material in a saccharidesolution to form a homogeneous saccharide coating on a surface of asolid support material, treating the solid support material having thesaccharide coating on the surface with a selenous acid solution, andheating the solid support material to form homogeneous seleniumnanomaterial on the surface of the solid porous support material.

In some embodiments, the pH of the selenous acid solution may be lessthan 3 or less than 1.6. The saccharide may include a monosaccharide, adisaccharide, or a polysaccharide, or a combination thereof. In someembodiments, the saccharide includes sucrose, or fructose, or acombination thereof. In some embodiments, the selenium nanomaterials mayhave a diameter from 10 nm to 1000 nm.

Other embodiments include articles made by the processes describedherein. In some embodiments, the article includes a solid materialhaving a selenium nanomaterial bound to a surface thereof made by theprocess including forming a saccharide coating on a surface of a solidsupport material, treating the solid support material having thesaccharide coating on the surface with a selenous acid solution, andheating the solid support material to form the selenium nanomaterial onthe surface of the solid porous support material. In some suchembodiments, the article may include less than 5% saccharide. Thesupport material may include activated carbon, a sponge, a film, afabric, a non-woven material, or a metal-organic framework (MOF), or acombination thereof.

Definitions

As used herein, “selenium nanomaterials” are meant to encompass seleniummaterials having at least one dimension less than 1 micrometer. Seleniumnanomaterials can exist in a variety of forms including, for example,nanospheres, nanofilms, nanorods, nanowires, nanostars, nanodomes, orcombinations thereof.

As used herein, “unbound selenium nanomaterials” is meant to encompassselenium nanomaterials within a material that are unbound or looselybound to a surface of the material. Typically, unbound seleniumnanomaterials can be removed from the surface of the material bytreating (e.g., rinsing or washing) the selenium nanomaterials withinthe material with an aqueous liquid.

As used herein, “selenium nanomaterials bound to a surface” is meant toencompass selenium nanomaterials within a material that are tightlybound to a surface of the material. Typically, selenium nanomaterialsbound to a surface cannot be readily removed from the surface of thematerial by treating (e.g., rinsing or washing) the seleniumnanomaterials within the material with an aqueous liquid.

The terms “comprises” and variations thereof do not have a limitingmeaning where these terms appear in the description and claims.

As used herein, “a,” “an,” “the,” “at least one,” and “one or more” areused interchangeably.

Also herein, the recitations of numerical ranges by endpoints includeall numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2,2.75, 3, 3.80, 4, 5, etc.).

The above brief description of various embodiments of the presentinvention is not intended to describe each embodiment or everyimplementation of the present invention. Rather, a more completeunderstanding of the invention will become apparent and appreciated byreference to the following description and claims in view of theaccompanying drawings. Further, it is to be understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the present invention.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows scanning electron microscopy images of an exemplary spongebefore (a) and after (b) immersion in nanoselenium (NanoSe) solution, asdescribed in Example 1. Materials shown in (b) were obtained from Method#1 of Example 1.

FIG. 2 shows scanning electron microscopy images (SEMs) of an exemplarycellulose sponge obtained using (a) Method #1, (b) Method #2, and (c)Method #3 of Example 1.

FIG. 3 shows scanning electron microscopy (SEM) images of an exemplarycellulose sponge obtained using Method #4 of Example 1.

FIG. 4 shows growth of monodisperse selenium nanospheres (50 nm to 500nm) on an exemplary natural honeycomb sponge.

FIG. 5 shows images of a water droplet on (a) an exemplary polyurethanesponge (“Sponge PU”) and (b) an exemplary natural honeycomb sponge(“Sponge PA”). The images are illustrative of the average contact angle.

FIG. 6 shows a Fourier transform infrared spectroscopy (FTIR) spectrumof Sponge PU of FIG. 5.

FIG. 7 shows a Fourier transform infrared spectroscopy (FTIR) spectrumof Sponge PA of FIG. 5.

FIG. 8 shows a photograph of an exemplary gold plated surface before(left) and after (right) coating with selenium nanomaterials.

FIG. 9 shows scanning electron microscopy (SEM) images of an exemplarygold plated surface before (a) and after (b,c) coating with seleniumnanomaterials.

FIG. 10 shows an exemplary gold plated glass before (left) and after(right) coating with a selenium nanofilm.

FIG. 11 shows scanning electron microscopy (SEM) images of (a) anexemplary gold plated glass, and an exemplary gold plated surfacetreated with selenous acid as described in Example 3 (b,c) without and(d, e) with sucrose.

FIG. 12 shows scanning electron microscopy (SEM) images of the growth ofselenium nanomaterials on an exemplary silicon surface using Method #7,described in Example 3.

FIG. 13 shows the size of selenium nanospheres that result in oneembodiment when the concentration of hydroquinone (HQ) is varied. Thesize of the nanospheres was measured by dynamic light scattering andconfirmed by scanning electron microscopy.

FIG. 14 shows a schematic representation of one embodiment of seleniumnanosphere formation on a sponge and then removal from the sponge.

FIG. 15 shows a sensitivity test using exemplary nanoselenium-coatedsponges and E. coli bacteria.

FIG. 16 shows exemplary scanning electron microscopy (SEM) images ofselenium nanoparticles grown on (a) a polyvinyl alcohol sponge, (b) anatural silk sponge, and (c) a polyurethane sponge using the processdescribed in Example 5.

FIG. 17 shows sponge-supported growth of colloidal selenium nanospheres(SeNS). (a) A photograph of a polyamide honeycomb sponge andcorresponding SEM images. (b) A polyamide honeycomb sponge after growthof SeNS with a combined hydrothermal/chemical reduction process, andcorresponding SEM images. (c) Retrieval of SeNS from the sponge into acolloidal solution and corresponding SEM images after deposition on asilicon substrate for visualization purposes.

FIG. 18 shows a Fourier transform infrared (FTIR) spectrum of anexemplary honeycomb sponge showing a mainly polyamide composition. Theinset depicts a water contact angle of 77°±5° for the same sponge.

FIG. 19 shows scanning electron microscope (SEM) images of oneembodiment of sponge-supported growth of SeNS using differentsaccharides: (a) lactose, (b) fructose, (c) glucose, and (d) sucrose asa sponge coating before synthesis.

FIG. 20 shows SEM images showing the effect of different sucroseconcentrations on the growth of SeNS on the sponge.

FIG. 21 shows the structure and composition of SeNS synthesized by thecombined hydrothermal/chemical reduction process. (a) TEM image of SeNSduring growth. Three types of nanoparticles can be identified in thehigh-resolution transmission electron microscopy (HRTEM) images: smallcrystalline SeNS (b1 and b2), large amorphous SeNS (c1 and c2), andmedium size amorphous SeNS (d). These particles incorporate smallcrystalline SeNS (e1, and e2). (f) EDX spectra showing the compositionof the three types of SeNS.

FIG. 22 shows Raman spectroscopy of exemplary selenium nanospheresshowing two peaks at 233 cm⁻¹ and 250 cm⁻¹ corresponding to crystallineselenium (c-Se) and amorphous selenium (a-Se) respectively. A shoulderpeak was also observed at 255 cm⁻¹ which corresponds to c-Se.

FIG. 23 shows growth mechanism of exemplary SeNS bydiffusion-internalization of smaller nanoparticles during thehydrothermal process. (a, b) SEM images of an exemplary sponge fiberafter the growth of SeNS with the hydrothermal process. (c) Evolution ofthe size of SeNS as a function of the incubation time of the sponge at110° C. The inset shows the corresponding SeNS solution retrieved fromthe sponges after incubation at different times. (d) SEM image showingthe agglomeration of small SeNS around particles. (e) TEM images show 10nm crystalline SeNS (arrows) incorporated by 100 nm amorphous SeNS,while 100 nm SeNS are internalized by bigger particles. (f) TEM imagesof amorphous SeNS internalizing a large number of crystalline SeNS (5-10nm). (g) TEM image of large amorphous SeNS internalizing smalleramorphous SeNS. (h1, h2, h3, h4) HRTEM images showing the change in thecrystalline structure or phase of 10 nm crystalline SeNS over time afterinternalization in bigger amorphous SeNS.

FIG. 24 shows an exemplary hydrothermal synthesis of SeNS at 110° C. fordifferent incubation times: (a) 5 minutes, (b) 10 minutes, and (c) 15minutes.

FIG. 25 shows a scheme representing one embodiment of a mechanism ofsponge-supported synthesis of crystalline (a) and amorphous (b, c) SeNS,during the combined hydrothermal and chemical reduction process. Thearrows show the direction of surface diffusion of the nanoparticles orgrowth species under the effect of heat and water evaporation.

FIG. 26 shows size control of SeNS grown by the combinedhydrothermal/chemical reduction process. (a) An image of SeNS obtainedfrom exemplary sponges treated with different hydroquinone (HQ)concentrations. (b) Correlation curve of the SeNS size as a function ofHQ concentration. (c) SEM images of the corresponding SeNS afterretrieval from the sponge and deposition on a silicon substrate.

FIG. 27 shows a solution of SeNS obtained with an exemplary combinedhydrothermal process/chemical reduction at hydroquinone concentration of5 M (a). The extrusion of the solution shown in (a) through a 400 nmfilter results in the separation of (b) small SeNS from (c) micrometricSeNS.

FIG. 28 shows scanning electron microscope (SEM) images of exemplarysponge-supported growth in a selenous acid solution having a pH from 1.6to 9.

FIG. 29 shows the effect of temperature on exemplary sponge-supportedgrowth of SeNS during the hydrothermal process.

FIG. 30 shows SEM images of commercially available selenium nanospheres.The solution was drop-casted on silicon substrate before (a) or after(b) 1.5 month of storage in solution.

FIG. 31 shows an exemplary Hg²⁺ adsorption isotherm for seleniumnanospheres. The inset depicts the linear regression obtained by fittingthe adsorption isotherm data with the Langmuir adsorption model.

FIG. 32 shows an exemplary polyurethane (PU) sponge (a) before and (b,c)after soaking (dip-coating) in a solution of selenium nanoparticles. Dipcoating yields surfaces with inhomogeneous coverage and nanoparticleaggregates.

FIG. 33 shows images of polyurethane (PU) and nanoselenium (NanoSe)sponges. (a) Photography of exemplary PU sponges before (white) andafter the growth of nanoselenium (brown). (b) SEM image of an exemplaryPU sponge. (c-e) SEM images of an exemplary NanoSe sponge. Thenanoselenium sponge can contain (c) selenium nanoparticles, (d) seleniumnanodomes, (e) or selenium nanofilms.

FIG. 34 shows an exemplary adsorption process and kinetics for exemplaryPU and NanoSe sponges. a) Adsorption kinetics of Hg²⁺ by PU (squares)and NanoSe sponges (circles) at an initial Hg²⁺ concentration of 10mg·L⁻¹. b) Plots of the pseudo-second order kinetic for Hg²⁺ adsorption.c) Adsorption isotherm of Hg²⁺ for an PU (squares) and a NanoSe spongewith 3% selenium (circles), and a NanoSe sponge with 50% selenium(triangles), and (d) the corresponding linear regression fitted usingthe Langmuir adsorption model.

FIG. 35 shows (a) Hg²⁺ binding interactions with the PU and NanoSesponges. (b) SEM image of a cross-section of the PU and NanoSe spongefibers. The dots show the localization of the energy-dispersive X-rayspectroscopy analysis (c) FTIR spectra of the PU sponge before and afterHg²⁺ adsorption.

FIG. 36 shows the effect of pH on Hg²⁺ sorption (left axis) for a NanoSesponge. The continuous lines (right axis) show the distribution of Hg²⁺chemical species depending on the pH.

FIG. 37 shows the selectivity of Hg²⁺ adsorption for PU and NanoSesponges. The same analysis was performed with (a) lake water and (b)drinking water. (c) Adsorption of other metal contaminants (Cu, Ni, Zn)by PU and NanoSe sponges. In all samples, the water was spiked with 10ppm mercury.

FIG. 38 shows the antimicrobial properties and cytotoxicity of PU(right, blue) and NanoSe (left, brown) sponges. (a) antimicrobial testsusing molds (C. guilliermondi), yeast (A. niger), gram-positive bacteria(Lactobacillus) and gram-negative bacteria (E. coli). (b) Cytotoxicityof PU and NanoSe sponges on mammalian cells with different exposuretimes. (c) Effect of the PU and NanoSe sponges, SeNPs, and NanoSe spongeladed with mercury on the catalytic activity of the enzyme glutathioneperoxidase.

FIG. 39 shows mercury ions released by the sponge after being washedwith nanopure water from 1 to 15 times. Each wash included soaking thesponge in nanopure water for a 5 seconds then squeezing it.

FIG. 40 shows growth of selenium nanomaterials on exemplary activatedcarbon materials. SEM images of activated carbon filter before (A1) andafter (A2) growth of nanoselenium. The image depicts the successfulgrowth of selenium nanoparticles and selenium nanofilms. SEM images ofactivated carbon pellets before (B1) and after (B2) growth ofnanoselenium. The images in B1 and B2 were obtained from a cross sectionof the activated carbon pellet, indicating that nanoselenium grows alsoinside the pellet bulk material.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present disclosure provides selenium nanomaterials, including, insome embodiments, selenium nanomaterials bound to a surface; methods ofpreparing selenium nanomaterials; and methods of using seleniumnanomaterials.

In some embodiments, the selenium nanomaterials and methods describedherein allow for the synthesis and storage of colloidal seleniumnanospheres directly on a substrate including, for example, a naturalhoneycomb sponge or a material including activated carbon. The methodsdescribed herein can yield nanoparticles from 10 nm to 1000 nm indiameter, enabling production of nanoparticles sized to meet the needsof a variety of biomedical, chemical, and electronic applications. Inaddition, the selenium nanomaterials and methods described herein allowfor the preservation of nanoparticle properties for over 8 months ofstorage without nanoparticle lyophilization that requirescryoprotectants or a time-consuming and costly freeze-dry process, andwithout specific coatings or solvents that may interfere withnanoparticle functionality, functionalization, and/or biocompatibility.

In some embodiments, the selenium nanomaterials described herein can beused as a mercury sorbent, exhibiting a mercury removal capacity of upto 1900 milligram (mg) Hg per gram (g) Se.

With increasing biomedical and engineering applications of seleniumnanospheres (SeNS), new efficient methods are needed for the synthesisand long-term preservation of these nanomaterials. Currently, SeNS aremostly produced through the biosynthesis route using microorganisms orby using wet chemical reduction, both of which have several limitationsin terms of nanoparticle size, yield, production time and long-termstability of the nanoparticles.

A number of different ways to synthesize, prepare and store seleniumnanomaterials have been proposed, but a number of challenges face anartisan seeking to synthesize selenium nanomaterials and, in particular,SeNS including the ability to efficiently produce a nanoparticle, theability to control the size of a nanoparticle, the ability to produce ananoparticle with minimum use of stabilizing agents, and the ability toproduce nanoparticles with long term stability. Size control isimportant not only because it allows tuning the optical properties ofthe nanospheres but also because the biological activity of SeNS can bedependent on their size (Peng et al., Journal of Inorganic Biochemistry,2007, 101, 1457-1463). Without stabilizing agents, the production andlong-term stability of single nanospheres (and not aggregates) hasproved challenging.

At the time of the invention, selenium nanospheres were produced using anumber of methods. Many reports used microbes, such as Pseudomonasalcaliphila, with metabolic systems that can reduce selenium sources toelemental selenium (Oremland et al. Microbiology, 2004, 70, 52-60;Shirsat et al., RSC Advances, 2015, 5, 92799-92811).

Although the microbial route of selenium nanospheres (SeNS) synthesis iseco-friendly, the synthesis requires several hours to several days forcell growth, yields polydisperse particles ranging from 50 nm to 500 nm,and the nanoparticles are produced with a natural coating ofextracellular polymeric substances (Jain et al. Environmental Science &Technology, 2015, 49, 1713-1720). This polymeric coating, while it helpsstabilize the particles, can also hinder the activity of the particlesand limit their use in certain applications like mercury capture wherethe surface of the nanoparticles needs to be accessible (Johnson et al.,Environmental Science & Technology, 2008, 42, 5772-5778).

Chemical reduction of selenous acid is another method used to prepareSeNS in the presence of a reducing reagent (e.g., hydrazine,hydroquinone, glucose, glutamic acid, and cysteine). Some methods,including some chemical reduction methods, used to prepare SeNS alsoinclude stabilizing agents such as polyvinyl alcohol, polyethyleneglycol, sodium dodecyl sulfate (SDS), bovine serum albumin (BSA),trypsin, and saccharides/polysaccharides. The reported sizes ofnanoparticles achieved by such methods range from 5 nm to 300 nm. Otherless common methods include hydrothermal and microwave-assistedsyntheses. Table 3 provides a comparison of the performance andlimitations of these different methods.

In contrast, and as further described below, the present disclosureprovides selenium nanomaterials and methods for making those seleniumnanomaterials that allow for a larger range of nanoparticle sizes, forthe preparation and storage of the selenium nanomaterials without theuse of a polymeric or proteinaceous stabilizing agent, and for highermercury sorption capacity.

Although numerous other materials and methods have been developed formercury (Hg) removal from water, high costs of the material and/or thelong contact time needed for mercury removal represent seriouslimitations for large scale implementation.

At the time of the invention, adsorption was the most widely used methodto remove mercury from water, and activated carbon was the commerciallyleading material, providing the ability to remove aqueous Hg to lessthan 0.2 μg/L. Although some commercially available technologies basedon sulfur-impregnated activated carbon claim a decrease of mercuryconcentrations from industrial wastewater to levels below 0.1 ppb, toachieve such results, the influent flow needs to be pretreated byadjusting the pH, for example, and the flow rate reduced to increase theadsorption contact time to 90 minutes (Tonini et al. EnvironmentalProgress 2003, 22(3): 167-173).

To increase the number of available adsorption sites and enhance theloading capacity, others have used nanomaterials such as graphene-basedcomposites, Mesoporous organosilica adsorbents, silica-titaniacomposites, and functionalized metal organic frameworks (MOFs). Althoughsome recently developed sulfur-functionized MOFs can achieve goodremoval rates, the high cost of the material and the long contact timeneeded for mercury removal represent serious limitations for large scaleimplementation.

In addition to the long contact time, the removal rate is important tomeeting regulatory requirements. While currently available technologiesare useful for reducing mercury in industrial wastewater where theconcentration ranges from 10 parts per trillion (ppt) to 50 parts perbillion (ppb), they are unable to completely clean the waters, and smallamounts of mercury are still discharged into the environment. Moreover,these technologies are not suitable for cleaning rain and surface waterswhere mercury concentrations range from 0.01 ppt to 100 ppt, and whereacceptable standard limits can be extremely low (e.g., 1.3 ng/L in theLake Superior Basin).

In addition to the performance, the hazardous nature of the sorbentwaste can increase the cost of disposal and limit the sustainability ofexisting technologies including the widely used sulfur-functionalizedsorbents. Despite the very high binding constants (10¹⁵-10¹⁷) ofsulfur-mercury (S—Hg) complexes, the S—Hg interaction is reversibleunder certain conditions, and can undergo ligand exchange reactions inaqueous solutions or biological systems (Karatza et al. ExperimentalThermal and Fluid Science 2000, 21(1-3): 150-155), which represents ahealth risk if the sorbent waste is released into the environment.

Selenium is known to capture mercury with exceptionally high bindingaffinity with a constant of 10⁴⁵, one-million-fold higher than thebinding affinity between mercury and sulfur (Khan et al. EnvironmentalToxicology and Chemistry 2009, 28(8): 1567-1577). As a result, theinteraction between Se and Hg yields a biologically stable SeHgprecipitates, with extremely low solubility (10⁻⁵¹ to 10⁻⁶⁵) as comparedto that of HgS precipitates (10⁻⁵²). Yet, in one instance only 7% of thepotential mercury removal capacity of selenium nanoparticles wasachieved, and the need to use nanoparticle aggregates instead of singlenanoparticles further reduced the surface area and removal rate (Johnsonet al. Environmental Science & Technology 2008, 42(15): 5772-5778; U.S.Pat. No. 8,491,865). Other attempts to use SeNPs-based sorbents reliedon first synthesizing and then adsorbing SeNPs on solid supports bysoaking (Johnson et al. Environmental Science & Technology 2008, 42(15):5772-5778; U.S. Patent Application No. 2012/0018384 A1; U.S. Pat. No.8,221,711; Huang et al. Journal of Chemical & Engineering Data 2015,60(1): 151-160). These processes result in anisotropic aggregates, poorsurface coverage and increased risk of leaching under acidic conditions,which could represent a secondary pollutant at high Se concentrations.

In contrast, and as further described below, the present disclosureprovides selenium nanomaterials bound to a surface and methods formaking those selenium nanomaterials that allow for efficient removal ofmercury, are suitable for cleaning rain and surface waters, and have adecreased risk of leaching under acidic conditions.

Selenium Nanomaterials

In one aspect, the present disclosure provides selenium nanomaterials,compositions including selenium nanoparticles, and articles includingselenium nanoparticles. Selenium nanomaterials can have a wide varietyof forms such as nanospheres, nanofilms, nanorods, nanowires, nanostars,nanodomes, or combinations thereof.

In some embodiments, the selenium nanomaterials preferably includeselenium nanospheres (SeNS). In some embodiments, a selenium nanospherecan have a hydrodynamic diameter of at least 5 nm, at least 10 nm, atleast 25 nm, at least 50 nm, at least 100 nm, at least 150 nm, at least200 nm, at least 300 nm, at least 400 nm, at least 500 nm, at least 600nm, at least 700 nm, at least 800 nm, at least 900 nm, or at least 1micrometer. In some embodiments, a selenium nanosphere can have anaverage particle size of up to 10 nm, up to 15 nm, up to 25 nm, up to 50nm, up to 100 nm, up to 150 nm, up to 200 nm, up to 300 nm, up to 400nm, up to 500 nm, up to 600 nm, up to 700 nm, up to 800 nm, up to 900nm, up to 1 micrometer, up to 1.1. micrometers, or up to 1.2micrometers.

In some embodiments, the selenium nanomaterials can be crystalline. Insome embodiments, the selenium nanomaterials can be amorphous. In someembodiments, a majority of the selenium nanomaterials can be amorphous.In some embodiments, the proportion of selenium nanomaterials that areamorphous increases as the size (e.g., hydrodynamic diameter) of theselenium nanomaterials increases.

In some embodiments, the selenium nanomaterials include less than 5% ofa monosaccharide, a disaccharide, and/or a polysaccharide; less than 3%of a monosaccharide, a disaccharide, and/or a polysaccharide; or lessthan 1% of a monosaccharide, a disaccharide, and/or a polysaccharide. Insome embodiments, a monosaccharide, a disaccharide, and/or apolysaccharide is present in the selenium nanomaterials in an amountinsufficient to act as a stabilizer.

In some embodiments, the selenium nanomaterials can exhibit a strongaffinity for mercury. In some embodiments, the selenium nanomaterialspreferably exhibit a maximal load or maximal removal capacity of atleast 1000 milligrams mercury per gram selenium (mg/g), at least 1200mg/g, at least 1500 mg/g, at least 1600 mg/g, at least 1700 mg/g, atleast 1800 mg/g, or at least 1900 mg/g. In some embodiments, theselenium nanomaterials preferably exhibit a maximal load or maximalremoval capacity of up to 1800 milligrams mercury per gram selenium(mg/g), up to 1900 mg/g, up to 2000 mg/g, up to 3000 mg/g, or up to 4000mg/g.

In some embodiments, the maximal load or maximal removal capacity can becalculated using the following equation:

$Q_{e} = {\frac{C_{i} - C_{f}}{m} \times V}$

where C_(i) is the initial concentration of mercury ions in the solution(mg/L), C_(f) is the final concentration of mercury ions in the solution(mg/L), m is the mass of adsorbent (g/L), V is the volume of thesolution (L), and Q_(e) is the amount of metal ion adsorbed in gram pergram of adsorbent at equilibrium (g/g).

In another aspect, the present disclosure provides an aqueous dispersionincluding selenium nanospheres, wherein the aqueous dispersion does notinclude a polymeric stabilizer or a proteinaceous stabilizer. In someembodiments, the aqueous dispersion includes less than 5% of amonosaccharide, a disaccharide, and/or a polysaccharide; less than 3% ofa monosaccharide, a disaccharide, and/or a polysaccharide; or less than1% of a monosaccharide, a disaccharide, and/or a polysaccharide. In someembodiments, a monosaccharide, a disaccharide, and/or a polysaccharideis present in the aqueous dispersion in an amount insufficient to act asa stabilizer.

In another aspect, the present disclosure provides a compositionincluding non-agglomerated selenium nanospheres, wherein the compositiondoes not include a polymeric stabilizer or a proteinaceous stabilizer.In some embodiments, the composition including non-agglomerated seleniumnanospheres includes less than 5% of a monosaccharide, a disaccharide,and/or a polysaccharide; less than 3% of a monosaccharide, adisaccharide, and/or a polysaccharide; or less than 1% of amonosaccharide, a disaccharide, and/or a polysaccharide. In someembodiments, a monosaccharide, a disaccharide, and/or a polysaccharideis present in the composition in an amount insufficient to act as astabilizer.

In some embodiments, selenium nanospheres—either alone or bound to thesurface of a material, as further described below—exhibit substantiallyirreversible binding with mercury. As used herein, “substantiallyirreversible binding” is meant to encompass selenium nanomaterials that,when bound to mercury, releases less than 10%, more preferably, lessthan 8%, and, even more preferably, less than 6% of the adsorbed mercurywhen exposed to harsh chemical treatments conventionally used forsorbent regeneration from mercury, including the use of thiourea, sodiumhydroxide, and/or 12 M hydrochloric acid.

Material Having a Surface

In some embodiments, the selenium nanomaterials are formed on and/or areassociated with a surface of a material. In some embodiments, theselenium nanomaterials are bound to the surface of the material. In someembodiments, the selenium nanomaterials are preferably unbound to thesurface of the material, that is the selenium nanomaterials can beremoved from the surface of the material by treating (e.g., rinsing orwashing) the selenium nanomaterials within the material with an aqueousliquid.

In some embodiments, the selenium nanomaterials can be present within anarticle including a material having unbound selenium nanospheres withinthe material. In some embodiments, the selenium nanomaterials can bepresent within an article including a material having seleniumnanomaterials bound to the surface thereof. In some embodiments, thearticle does not include a polymeric stabilizer. In some embodiments,the article does not include a proteinaceous stabilizer. In someembodiments, the article includes less than 5% of a monosaccharide, adisaccharide, and/or a polysaccharide; less than 3% of a monosaccharide,a disaccharide, and/or a polysaccharide; or less than 1% of amonosaccharide, a disaccharide, and/or a polysaccharide. In someembodiments, a monosaccharide, a disaccharide, and/or a polysaccharideis present in the article and/or the material in an amount insufficientto act as a stabilizer.

In some embodiments, the article includes less than 50% w/w, less than40% w/w, less than 30% w/w, less than 20% w/w, less than 10% w/w, lessthan 5% w/w, less than 4% w/w, less than 3% w/w, less than 2% w/w, orless than 1% w/w of selenium nanomaterials. In some embodiments, thearticle includes at least 0.5% w/w, at least 1% w/w, at least 2% w/w, atleast 3% w/w, at least 4% w/w, at least 5% w/w, at least 10% w/w, atleast 20% w/w, at least 30% w/w, or at least 40% w/w of seleniumnanomaterials. In some embodiments, the article and/or the materialpreferably include activated carbon.

In some embodiments, the material preferably provides a porous solidsupport including, for example a sponge. In some embodiments, thesurface of the material is capable of providing nucleation sites forformation of the selenium nanomaterial.

Suitable materials can be selected from a wide variety of materialsincluding organic materials, inorganic materials, and combinationsthereof. Exemplary materials include, but are not limited to, sponges,films, fabrics, non-woven materials, metal-organic frameworks (MOF),activated carbon, and combinations thereof. Exemplary films include, butare not limited to, silicon substrates, glass, metal films, activatedcarbons, polymeric films, and combinations thereof.

In some embodiments, the material includes an activated carbon. Theactivated carbon can be in any useful form including, for example, apellet, a scrubber, or a filter.

In some embodiments, the material preferably includes a polyamide. Insome embodiments, the material includes a scleroprotein including, forexample, a spongin. In some embodiments, the material preferablyincludes a natural honeycomb marine sponge (e.g., a member of the phylumPorifera, including, for example, a member of the Demospongiae class).

Optionally, the surface can be a hydroxylated surface. Exemplarymaterials having a hydroxylated surface include, but are not limited to,materials treated with a monosaccharide, a disaccharide (e.g., sucrose),and/or a polysaccharide. In some embodiments, the hydroxylated surfaceis preferably provided by a saccharide containing fructose including,e.g., fructose, sucrose, lactulose, turanose etc.

In some embodiments, the material preferably includes a homogeneoussaccharide coating on a surface, and even more preferably, a homogenouscoating of sucrose.

In some embodiments, the material can include a surface having a watercontact angle less than 90 degrees or, more preferably, less than 80degrees. In some embodiments, such surfaces can be capable of providingnucleation sites to provide unbound selenium nanomaterials. A widevariety of materials having a water contact angle less than 90 degreescan be used. Exemplary materials having a water contact angle less than90 degrees include, but are not limited to, hydrophilic materials suchas polyamide materials which can be, for example, in the form of anatural honeycomb sponge. Certain natural honeycomb sponges that have apolyamide content of about 60 wt.-% have been determined to have a watercontact angle of 77 degrees±5 degrees.

One of skill in the art would recognize that water contact angles can bereadily measured using well known methods to determine if the watercontact angle is less than 90 degrees or greater than 90 degrees.Exemplary methods include, but are not limited to, goniometry.

In some embodiments, the material can include a surface having a watercontact angle greater than 90 degrees. In some embodiments, suchsurfaces can be capable of providing nucleation sites to provideselenium nanomaterials bound to a surface. A wide variety of materialshaving a water contact angle greater than 90 degrees can be used.Exemplary materials having a water contact angle greater than 90 degreesinclude, but are not limited to, hydrophobic materials such aspolyurethane materials which can be, for example, in the form of asynthetic sponge. Certain polyurethane synthetic sponges have beendetermined to have a water contact angle of 140±5 degrees.

In some embodiments, a material having selenium materials bound to asurface thereof can exhibit a distribution coefficient, K_(d) of atleast 1*10⁸ mL·g⁻¹, at least 5*10⁸ mL·g⁻¹, or at least 1*10⁹ mL·g⁻¹,where (K_(d)) is defined as:

$K_{d} = {\frac{( {C_{o} - C_{f}} )}{C_{f}} \times \frac{V}{m}}$

where C₀ is the initial Hg²⁺ concentration, C_(f) is the finalequilibrium Hg²⁺ concentration. Since removal rate for a NanoSe spongeis, in some embodiments, 100%, the concentration of 0.2 ng·L⁻1 was takenas C_(f) since it represents the limit of detection of the equipmentused for mercury detection. V is the volume of the solution in mL, and mis the mass of sorbent in g. In some embodiments, including, forexample, where the material is a polyurethane sponge, the K_(d) can beat least 1*10⁹ mL·g⁻¹. In one embodiment, K_(d) can be 1.67×10⁹ mL·g⁻¹,two orders of magnitude higher than the best values reported for Hg²⁺sorbents at the time of the invention (Zhang et al. Nat. Commun. 2014,5:5537).

In some embodiments, this K_(d) is preferably achieved withoutpretreatment including, for example, pH modification.

In some embodiments, a material having selenium materials bound to asurface thereof can achieve up to 60%, up to 65%, up to 70%, up to 75%,or up to 80%, of its maximal removal capacity within 1 second. In someembodiments, a material having selenium materials bound to a surfacethereof can achieve up to 85%, up to 90%, up to 95%, up to 98%, or up to99% of its maximal removal capacity within 500 seconds. In someembodiments, a material having selenium materials bound to a surfacethereof can achieve up to 85%, up to 90%, up to 95%, up to 98%, up to99%, or up to 100% of its maximal removal capacity within 3600 seconds(1 hour).

In some embodiments, the material can include fibers. In someembodiments, the fibers can have a diameter of at least 5 μm, at least10 μm, or at least 15 μm. In some embodiments, the fibers can have adiameter of up to 15 μm, up to 20 μm, up to 25 μm, up to 30 μm, up to 40μm, or up to 50 μm. In some embodiments, the fibers preferably have adiameter in a range of 10 m to 30 μm.

In some embodiments, the material can have a surface roughness of atleast 5 nm, at least 10 nm, at least 15 nm, at least 20 nm, at least 30nm, at least 40 nm, or at least 50 nm. In some embodiments, the materialcan have a surface roughness of up to 15 nm, up to 20 nm, up to 30 nm,up to 40 nm, up to 50 nm, or up to 100 nm.

In some embodiments, the material preferably has a surface roughness ina range of 10 nm to 20 nm.

In some embodiments, the material has a high surface to volume ratio. Insome embodiments, the material preferably permits bulk diffusion ofmercury into the material.

In some embodiments, and as further described below, using seleniumnanomaterials that are formed on and/or are associated with a surface ofa material can increase long term stability of the nanomaterials. Insome embodiments, the long-term stability can be determined by measuringthe change in nanoparticle size, zeta potential, and/or monodispersityover time. In some embodiments, the nanomaterials described herein arestable for at least 3 months, at least 5 months, at least 6 months, atleast 7 months, at least 8 months, at least 9 months, at least 12months, or at least 24 months. In some embodiments, the nanomaterialsdescribed herein are stable for up to 8 months, up to 9 months, up to 12months, up to 24 months, or up to 36 months. In some embodiments, ananomaterial that is “stable” can be defined as a nanomaterial thatexhibits a change in the average size of the nanomaterials of less than10%, less than 8%, or less than 5%. In some embodiments, a nanomaterialthat is “stable” can be defined as a nanomaterial that exhibits a changein zeta potential of less than 15%, less than 10%, or less than 5% overa defined period of time. In some embodiments, a nanomaterial that is“stable” can be defined as a nanomaterial that exhibits a change in thepolydispersity index (PDI) of the nanomaterial of less than 15%, lessthan 13%, less than 12%, or less than 10% over a defined period of time.

In some embodiments, and as further described below, using seleniumnanomaterials that are formed on and/or are associated with a surface ofa material can increase Se—Hg interactions.

Methods of Making Selenium Nanomaterials

In another aspect, the present disclosure provides methods of preparingselenium nanomaterials including, for example, selenium nanoparticles.

In some embodiments, the methods of preparing a selenium nanomaterialinclude: treating a material with a selenous acid solution, and heatingthe material to form the selenium nanomaterial on a surface of thematerial.

In some embodiments, the methods of preparing a selenium nanomaterialinclude combining an aqueous solution of selenous acid with an aqueoussolution of a reducing agent in the presence of a material underconditions effective to form the selenium nanomaterial on a surface ofthe material.

The material can include any of the materials described in thisdisclosure. The selenium nanomaterial can include any of the seleniumnanomaterials described in this disclosure.

In some embodiments, the method includes treating the surface to form ahydroxylated surface. In some embodiments, immobilizing selenous acid ona material includes treating the material by soaking it and/or immersingit in a saccharide solution. In some embodiments, the method includesforming a saccharide coating on a surface of the material. In someembodiments, the saccharide coating is preferably homogeneous.

A saccharide can include, for example, monosaccharide (e.g., fructose),a disaccharide (e.g., sucrose), and/or a polysaccharide. In someembodiments, the hydroxylated surface is preferably provided by asaccharide containing fructose including, e.g., fructose, sucrose,lactulose, turanose etc.

Exemplary saccharide solutions can have a concentration of at least 1percent (%) saccharide, at least 5% saccharide, at least 10% saccharide,at least 15% saccharide, at least 20% saccharide, at least 25%saccharide, at least 30% saccharide, at least 40% saccharide, or atleast 50% saccharide. Exemplary saccharide solutions can have aconcentration of up to 5% saccharide, up to 10% saccharide, up to 15%saccharide, up to 20% saccharide, up to 25% saccharide, up to 30%saccharide, up to 40% saccharide, up to 50% saccharide, up to 60%saccharide, up to 80% saccharide, or up to 95% saccharide. In someembodiments, including, the saccharide solution can have a concentrationin a range of 20% to 30% saccharide or, in some embodiments, aconcentration of 25% saccharide.

The material may be treated with a saccharide solution for a wide rangeof times, as desired. For example, the material may be treated for atleast 1 minute, at least 3 minutes, at least 5 minutes, at least 7minutes, at least 9 minutes, at least 10 minutes, at least 12 minutes,at least 15 minutes, at least 20 minutes, or at least 30 minutes. Forexample, the material may be heated for up to 10 minutes, up to 15minutes, up to 20 minutes, up to 25 minutes, up to 30 minutes, up to 40minutes, up to 50 minutes, or up to 60 minutes. In some embodiments, thematerial can be treated with a saccharide solution for a time in a rangeof 10 minutes to 30 minutes or, in some embodiments, for 15 minutes.

In some embodiments, the method can further include removing excesssolution from the material after treatment to form a hydroxylatedsurface. For example, in embodiments when the material is a sponge, thesponge can be squeezed.

In some embodiments, treating the material with a selenous acid solutionincludes immobilizing selenous acid on a material. In some embodiments,treating the material with a selenous acid solution includes forming athin film of selenous acid on a material. In some embodiments, theselenous acid solution is preferably an aqueous solution. In someembodiments, an aqueous selenous acid solution can have a concentrationof at least 0.1 M, at least 0.5 M, at least 1 M, at least 2 M, at least3M. In some embodiments, an aqueous selenous acid solution can have aconcentration of up to 1 M, up to 2 M, up to 3M, up to 4 M, up to 5 M,up to 6M, or up to 7M, In some embodiments, an aqueous selenous acidsolution can have a concentration in a range of 0.1 M to 6 M. In someembodiments, an aqueous selenous acid solution may preferably have aconcentration of 1.4 M. In some embodiments, the material can beimmersed in the selenous acid solution. Without wishing to be bound bytheory, it is believed that a hydroxylated surface including, forexample, a homogeneous sucrose coating on the surface of the material,allows isotropic immobilization of the selenous acid ions by interactionwith hydroxyl groups, thus promoting a homogenous growth ofnanomaterials. For example, in some embodiments, a homogeneous sucrosecoating on a sponge can immobilize selenous acid ions by interactionwith sucrose hydroxyl groups, promoting a homogenous growth ofnanoparticles.

The material may be treated with a selenous acid solution for a widerange of times, as desired. For example, the material may be treated forat least 1 minute, at least 3 minutes, at least 5 minutes, at least 7minutes, at least 9 minutes, at least 10 minutes, at least 12 minutes,at least 15 minutes, at least 20 minutes, or at least 30 minutes. Forexample, the material may be heated for up to 10 minutes, up to 15minutes, up to 20 minutes, up to 25 minutes, up to 30 minutes, up to 40minutes, up to 50 minutes, or up to 60 minutes. In some embodiments, thematerial can be treated with a selenous acid solution for a time in arange of 20 minutes to 40 minutes or, in some embodiments, for 25minutes or for 30 minutes.

The method of preparing a selenium nanomaterial can be carried out at awide range of pH conditions as desired. In some embodiments, however,the pH of a selenous acid solution is preferably less than 3, morepreferably less than 2.5, or even more preferably less than 2. In someembodiments, the pH of a selenous acid solution is preferably 1.6.

In some embodiments, the conditions effective to form seleniumnanomaterials comprise a temperature of 35° C. to 170° C. In someembodiments, a method of preparing selenium nanomaterials includesheating and/or drying the material. In some embodiments, the materialmay be dried in an oven including, for example, a vacuum oven. Thematerial may be heated at a wide range of temperatures as desired. Insome embodiments, the material is preferably heated at a temperaturegreater than the glass transition temperature of amorphous selenium (31°C.±0.5° C.). In some embodiments, the material may be heated at atemperature and time sufficient to form selenium nanomaterials having anaverage size of 50 nm to 150 nm. In some embodiments, the material maybe heated at a temperature of at least 30° C., at least 31° C., at least35° C., at least 40° C., at least 45° C., at least 50° C., at least 55°C., at least 60° C., at least 65° C., at least 70° C., at least 75° C.,at least 80° C., at least 90° C., at least 100° C., at least 110° C., orat least 120° C. In some embodiments, the material may be heated at atemperature of up to 40° C., up to 45° C., up to 50° C., up to 55° C.,up to 60° C., up to 65° C., up to 70° C., up to 75° C., up to 80° C., upto 90° C., up to 100° C., up to 110° C., up to 120° C., up to 130° C.,up to 140° C., up to 150° C., up to 170° C., or up to 200° C. Thematerial may be treated with heat for a wide range of times, as desired.For example, the material may be heated for at least 1 minute, at least3 minutes, at least 5 minutes, at least 7 minutes, at least 9 minutes,at least 10 minutes, at least 12 minutes, at least 15 minutes, at least20 minutes, or at least 30 minutes. For example, the material may beheated for up to 10 minutes, up to 15 minutes, up to 20 minutes, up to25 minutes, up to 30 minutes, up to 40 minutes, up to 50 minutes, or upto 60 minutes. In some embodiments including, for example, when thematerial is a natural honeycomb sponge, the material may be dried in avacuum oven (at −2.6 kPa) for 10 minutes at 110° C. In some embodimentsincluding, for example, when the material is a polyurethane sponge, thematerial may be dried in an oven or 2 minutes at 100° C.

In some embodiments, including, for example, when a nanoparticle havingan average size of 150 nm or less is desired, the temperature ispreferably in a range of 110° C. to 120° C. In some embodiments,increases in temperature or in the time the material is heated or bothresult in an increase in nanoparticle size. In some embodiments,increases in temperature or in the time the material is heated or bothresult in an increase in selenium content in the material.

Without wishing to be bound by theory, it is believed that when theselenous acid treated material is heated, the selenium ions present arereduced to elemental selenium (Se⁰). While the reduction is believed toprimarily be caused by the heating, mild vacuum conditions can expediteevaporation of water including, for example, when the material is asponge. The reduced selenium ions then diffuse and crystalize on thesurface of the material under the effect of heat and rapid waterevaporation. Surface diffusion of the reduced selenium ions can resultin instantaneous growth of 5 nm to 10 nm crystalline SeNS. SeNS having adiameter of 50 nm to 150 nm can be observed after about 5 minutes oftreatment. In certain embodiments, increasing the time during which thematerial is exposed to heat has been found to result in increasing thesize of selenium nanomaterials (e.g., spherical particles).

In certain embodiments, the methods include treating the material with areducing agent. In some embodiments, treating with a reducing agent canform and/or increase the size of the selenium nanomaterials. In someembodiments, the reducing agent is preferably in a solution. Forexample, the material may be immersed in a solution including a reducingagent including, for example, an aqueous solution. In some embodiments,for example, initiating or maintaining nanomaterial growth on thematerial can include immersing the material in a reducing agentsolution. A wide variety of reducing agents can be used. Useful reducingagents include, for example, acidic compounds. Exemplary reducing agentsinclude, but are not limited to, hydroquinone, acetic acid, glutathione,and combinations thereof. In some embodiments, the reducing agentsolution preferably includes hydroquinone.

Useful concentrations of reducing agents will depend on the reactionconditions and the specific reducing agent being used. For example, whenthe reducing agent includes hydroquinone, hydroquinone concentrations of0.1 M to 6 M in the solution can be used. For example, the concentrationof the reducing agent can be in a range of 0.1 M to 6 M including, forexample, at least 0.1 M, at least 0.2 M, at least 0.3 M, at least 0.4 M,at least 0.5 M, at least 0.6 M, at least 0.7 M, at least 1.0 M, at least1.5 M, at least 2.0 M, at least 3.0 M, at least 4.0 M, at least 5.0 M,at least 5.5 M, or at least 6 M or up to 0.2 M, up to 0.2 M, up to 0.3M, up to 0.4 M, up to 0.5 M, up to 0.6 M, up to 0.7 M, up to 1.0 M, upto 1.5 M, up to 2.0 M, up to 3.0 M, up to 4.0 M, up to 5.0 M, up to 5.5M, up to 6 M, or up to 7 M. In certain embodiments, increasingconcentrations of reducing agent (e.g., hydroquinone) have been found toresult in increasing sizes of selenium nanomaterials (e.g., sphericalparticles), as shown where the reducing agent is hydroquinone in FIG.26.

In some embodiments, treating with a reducing agent preferably includesheating the material and the reducing agent at a temperature greaterthan the glass transition temperature of amorphous selenium (31° C.±0.5°C.). For example, the material while placed in a solution includingreducing agent can be heated on a hot plate, in a water bath, and/or inan incubator. In some embodiments, the reducing agent may be preheatedbefore being added to the material to a temperature of at least 30° C.,at least 31° C., at least 35° C., at least 40° C., at least 45° C., atleast 50° C., at least 55° C., at least 60° C., at least 65° C., atleast 70° C., at least 75° C., at least 80° C., at least 90° C., atleast 100° C., at least 110° C., or at least 120° C. When the reducingagent is hydroquinone, a hydroquinone solution may preferably bepreheated to a temperature greater than the crystallization temperatureof hydroquinone. In some embodiments, a hydroquinone solution maypreferably be preheated to a temperature of at least 65° C.

In some embodiments, the material may be heated at a temperature of atleast 30° C., at least 31° C., at least 35° C., at least 40° C., atleast 45° C., at least 50° C., at least 55° C., at least 60° C., atleast 65° C., at least 70° C., at least 75° C., at least 80° C., atleast 90° C., at least 100° C., at least 110° C., or at least 120° C. Insome embodiments, the material may be heated at a temperature of up to40° C., up to 45° C., up to 50° C., up to 55° C., up to 60° C., up to65° C., up to 70° C., up to 75° C., up to 80° C., up to 90° C., up to100° C., up to 110° C., up to 120° C., up to 130° C., up to 140° C., upto 150° C., up to 170° C., or up to 200° C. In some embodiments,increases in temperature or in the time the material is heated or bothresult in an increase in nanoparticle size. In some embodiments,increases in temperature or in the time the material is heated or bothresult in an increase in selenium content in the material.

In some embodiments, the material may be heated to a temperature of atleast 30° C., at least 31° C., at least 35° C., at least 40° C., atleast 45° C., at least 50° C., at least 55° C., at least 60° C., atleast 65° C., at least 70° C., at least 75° C., at least 80° C., atleast 90° C., at least 100° C., at least 110° C., or at least 120° C. Insome embodiments, the material may be heated to a temperature of up to40° C., up to 45° C., up to 50° C., up to 55° C., up to 60° C., up to65° C., up to 70° C., up to 75° C., up to 80° C., up to 90° C., up to100° C., up to 110° C., up to 120° C., up to 130° C., up to 140° C., upto 150° C., up to 170° C., or up to 200° C.

The material may be treated with a reducing agent and/or heated for awide range of times, as desired. For example, the material may be heatedfor at least 1 minute, at least 3 minutes, at least 5 minutes, at least7 minutes, at least 9 minutes, at least 10 minutes, at least 12 minutes,at least 15 minutes, or at least 20 minutes. For example, the materialmay be heated for up to 10 minutes, up to 15 minutes, up to 20 minutes,up to 25 minutes, or up to 30 minutes.

In an exemplary embodiment, a sponge can be treated with a 2.2 Mhydroquinone solution for 5 minutes at 65° C.

Without wishing to be bound by theory, it is believed that treating thematerials at a temperature greater than the glass transition temperatureof selenium can be improve or increase the binding selenium to thematerial and/or can produce nanoselenium materials that favors highsubsurface and bulk diffusion of mercury. The high subsurface and bulkdiffusion of mercury increase the loading capacity of the materialincluding, for example, by allowing at least 70% of selenium atoms tointeract with and capture (bind to) mercury.

In some embodiments, the method further includes immersing the materialin a composition including selenium ions during and/or after thematerial has been treated with a reducing agent. In some embodiments,the material can be immersed in a selenous acid solution. In someembodiments, the material can be immersed in a selenous acid solutionafter being treated with a reducing agent. In some embodiments, thematerial can be treated in a solution that includes selenous acid and areducing agent at temperatures greater than 35° C. In some embodiments,the selenous acid solution can be preheated to a temperature greaterthan 35° C. before being placed in contact with the material. Theselenous acid solution can in some embodiments be identical to theselenous acid solution used on the material before the material wastreated with a reducing agent. The selenous acid solution can in someembodiments be the same selenous acid solution used on the materialbefore the material was treated with a reducing agent.

In certain embodiments, conditions effective to form the seleniumnanomaterials include the substantial absence of a polymeric stabilizer.As used herein, the “substantial absence” of a polymeric stabilizermeans that a polymeric stabilizer has not been intentionally added, and,if present, is preferably present at less than 5 wt.-%. Methods ofpreparing selenium nanomaterials known in the art have used polymericstabilizers such as polyvinyl alcohol, polysaccharides, and chitosan.

In certain embodiments, conditions effective to form the seleniumnanomaterials include the substantial absence of a proteinaceousstabilizer. As used herein, the “substantial absence” of a proteinaceousstabilizer means that a proteinaceous stabilizer has not beenintentionally added, and, if present, is preferably present at less than5 wt.-%. Methods of preparing selenium nanomaterials known in the arthave used proteinaceous stabilizers such as BSA.

In certain embodiments, conditions effective to form the seleniumnanomaterials include the use of a monosaccharide, a disaccharide,and/or a polysaccharide. In certain embodiments, conditions effective toform the selenium nanomaterials include the substantial absence of asaccharide/polysaccharide stabilizer. As used herein, the “substantialabsence” of a saccharide/polysaccharide stabilizer means that asaccharide has not been added to act as a stabilizer, and, if present,is preferably present at less than 5 wt.-%. In some embodiments, amonosaccharide, a disaccharide, and/or a polysaccharide is present inthe material in an amount insufficient to act as a stabilizer.

Selenium nanomaterials formed by the methods disclosed herein can have awide variety of forms such as nanospheres, nanofilms, nanorods,nanowires, nanostars, nanodomes, or combinations thereof.

In a further aspect, the present disclosure provides a method ofpreparing selenium nanomaterials including combining an aqueous solutionof selenous acid with an aqueous solution of a reducing agent in thepresence of a surface capable of providing nucleation sites underconditions effective to form selenium nanomaterials.

In some embodiments, methods of preparing selenium nanomaterials canfurther include preparing a dispersion of selenium nanomaterials (e.g.,selenium nanospheres). In one embodiment, the method includes treatingthe material with an aqueous liquid to provide a dispersion of theselenium nanomaterials. In some embodiments, the material preferably hasunbound selenium nanomaterials within the material prior to treatmentwith the aqueous liquid.

In some embodiments, methods of preparing selenium nanomaterials canfurther include includes quenching and/or washing the materialincluding, for example, in an ice bath or with nanopure water. In someembodiments, the material preferably has bound selenium nanomaterials.

In some embodiments, the method further includes separating thedispersion of selenium nanomaterials by size. A variety of techniquesmay be used to separate nanomaterials of different sizes including, forexample, centrifugation or filtration.

In some aspects, the present disclosure provides a method of preparingunbound selenium nanomaterials. In one embodiment, the method includescombining an aqueous solution of selenous acid with an aqueous solutionof a reducing agent in the presence of a surface capable of providingnucleation sites under conditions effective to form seleniumnanomaterials, wherein the surface capable of providing nucleation sitesis provided by a material having a water contact angle of less than 90degrees.

In another aspect, the present disclosure provides a method of preparingselenium nanomaterials bound to a surface. In one embodiment, the methodincludes: combining an aqueous solution of selenous acid with an aqueoussolution of a reducing agent in the presence of a surface capable ofproviding nucleation sites under conditions effective to form seleniumnanomaterials, wherein the surface capable of providing nucleation sitesis provided by a material having a water contact angle of greater than90 degrees.

Methods of Using Selenium Nanomaterials Bound to a Surface

In another aspect, the present disclosure provides methods for using theselenium nanomaterial described herein.

Mercury Removal

In one aspect, the present disclosure provides a method for removingmercury from air or water, the method includes exposing the air or waterto any one of the articles, dispersions, or compositions comprisingselenium nanomaterials disclosed herein.

In some embodiments, the method includes removing at least 95%, at least98%, at least 99%, at least 99.5%, at least 99.9%, and/or up to 100% ofmercury from contaminated water. For example, a method could includeremoving mercury from water contaminated having 10 ppm mercury to yieldwater having less than 0.004 ppm mercury.

Anti-Microbial Applications

In another aspect, the present disclosure provides a method of killingor inhibiting the growth of microorganisms, the method includingexposing the microorganisms to any one of the articles, dispersions, orcompositions comprising selenium nanomaterials disclosed herein.

For example, a material including selenium nanomaterials can be used inbuilding systems (e.g., joints, ventilation systems, pipes, humid areas)to prevent the growth of molds. In some embodiments, a sponge or othermaterial including selenium nanomaterials described herein can be usedfor surface cleaning.

The present invention is illustrated by the following examples. It is tobe understood that the particular examples, materials, amounts, andprocedures are to be interpreted broadly in accordance with the scopeand spirit of the invention as set forth herein.

EXAMPLES Example 1

I. Invention and Products Disclosed:

-   -   a. Methods of growing nanoselenium (NanoSe films or        nanostructures) on different support including porous materials        (sponges, metal-organic frameworks, . . . ), thin films and        surfaces (glass, silicon, . . . ),    -   b. Devices that can be used to remove mercury from wastewater,        stormwater ponds, wetlands and from surface waters such as lakes        and rivers.    -   c. Products treated with our methods to provide new properties        or functionalities    -   d, Methods for producing colloidal selenium nanospheres (SeNS)

II. Supported Growth of NanoSe Materials and Application for MercuryRemoval

1. Summary

Selenium (Se) interacts strongly with mercury (Hg) and forms inert andnon-toxic precipitates (SeHg).[1] The use of selenium nanomaterials cansignificantly increase the surface area of this interaction and enableenhanced mercury removal from contaminated water and gas. Here, wereport novel methods to grow nanoselenium (NanoSe), including seleniumnanoparticles (SeNP) and selenium nanofilms (SeNF) directly on organicor inorganic supports (sponge, metal organic frameworks, and otherporous materials). This development will lead to the design of newsystems and devices for mercury removal from water and flue gases. Aproof of concept have been demonstrated by the development of aNanoSelenium Sponge capable of removing over 99.95% of mercury fromwater within few minutes and before even we optimize the process. Beyondmercury removal, the developed SeNP and SeNF processes can findapplications in catalysis, solar cells, surface coating and otherindustries where selenium is used.

2. Statement of Need and Significance:

The urgent need for cost-effective mercury removal technologies isclearly justified by the major ad global threat that mercury causes toaquatic life but also to human health by entering the food chain. Twothirds of the waters on Minnesota's 2004 Impaired Waters List areimpaired because of mercury contamination that ranges from 0.27 to 12.43ng/L (the EPA limit is 2 ng/L).[2] Mercury contamination of lake watersresults in mercury accumulation in fish, leading the MinnesotaDepartment of Health to establish fish consumption guidelines. A numberof fish species store-bought or caught in Minnesota lakes are notadvised for consumption more than once a week or even once a month. InMinnesota's North Shore, 10% of tested newborns had mercuryconcentrations above the EPA reference dose for methylmercury (the formof mercury found in fish).[3] This means that some pregnant women in theLake Superior region, and in Minnesota, have mercury exposures that needto be reduced.

3. State of the Art in Mercury Removal

A number of technologies have been developed to remove mercury fromwater, including Precipitation/coprecipitation, adsorption, membranefiltration, and biological treatment.[4]

In 2007, a company named Pacific Northwest National Laboratory (PNNL)developed a new method on pilot scale. They prepared ThiolsSelf-Assembled Monolayers on Mesoporous Silica (Thiol SAMMS) to removemercury from industrial waste. Their method showed efficiency around 0.2ppm [5]. The role of thiols in capturing mercury is very welldocumented. With the increased interest in metal organic frameworks andporous organic polymers (MOFs and POPs), numerous groups have preparedthiol containing MOFs and POPs to capture mercury from water and vapors[6-10]. However, beside the high cost of these technologies to operateon a large scale, they are based on capturing mercury with instablecomplexes that could represent health risk when leaked into theenvironment. The novel sponge technology is extremely cost-effective andis based on the formation of permanent and non-toxic complexes ofmercury with other materials.

4. Technology Description

4.1. Concept and Innovative Aspects

To the best of our knowledge, this work is the first to grownanoselenium materials directly on solid supports including sponge andother porous materials and surfaces. Most reported research inliterature synthesize their selenium nanoparticles first and thenimmerse the material to be coated in the nanoparticle solution. Thisalso the first use of nanoselenium sponge to remove mercury from water.Another innovative aspect is the production of large colloidal seleniumnanospheres (50-500 nm) with chemical synthesis, without using microbialprocesses as it is currently done.

4.2. Competitive Advantages of Using NanoSe

-   -   The most commonly used mercury sorbents are based on        thiol-functionalized materials such as activated carbon.        However, despite the very high formation constants (10¹⁵-10¹⁷)        of thiol-mercury (S—Hg) complexes, [64] the S—Hg interaction is        extremely labile and can undergo rapid ligand exchange reactions        in aqueous solutions or biological systems [67-70], which causes        a high risk if the activated carbon materials are released into        the environment. Selenium is known to capture mercury with        exceptionally high binding affinity with a constant of 10⁴⁵;        one-million-fold higher than the binding affinity between Hg and        sulfur which is largely used in mercury sorbents.[11] As a        result, the interaction between Se and Hg yields a biologically        inert and stable SeHg precipitates, with extremely low        solubility (10⁻⁵⁸ to 10⁻⁶⁵) as compared to that of HgS        precipitates (10⁻⁵²),[1] and thus present a much lower health        risk.    -   The use of NanoSe significantly increases the surface area for        Se—Hg interaction and thus improves the removal capacity for        mercury.

4.3. Advantages of Growing NanoSe Directly on Solid Supports

-   -   Easy, rapid and cheap growth procedures    -   Homogenous coverage    -   No leakage of selenium particles after washing or during use    -   Monodisperse nanostructures    -   A variety of shapes including nanoparticles, microspheres and        nanodomes    -   Possibility to produce nanoselenium thin films    -   In the case of mercury capture, the nanoselenium sponge will        make it easy to collect mercury and dispose it for further        treatment without a risk of leakage into the environment.    -   Today, nanoselenium is used in form of aggregates for mercury        capture (sometimes called unstabilized nanoselenium) [12, 13].        When single selenium    -   Possibility to produce nanoselenium thin films    -   In the case of mercury capture, the nanoselenium sponge will        make it easy to collect mercury and dispose it for further        treatment without a risk of leakage into the environment.    -   Today, nanoselenium is used in form of aggregates for mercury        capture (sometimes called unstabilized nanoselenium).[12, 13].        When single selenium nanoparticle are stabilized by coating them        with a ligand, the nanoparticles become ineffective for mercury        capture, probably due to inaccessibility of mercury to the        selenium surface. Growing selenium nanoparticles on solid        supports such sponge allows the use of single nanoparticles (not        aggregates) and thus dramatically increases the surface area for        mercury capture.

4.4. Experimental Procedures and Results

a. Conventional Procedure for Nanoselenium Synthesis

Conventional synthesis of nanoselenium particles was performed accordingto Kumar et al [14]. By using selenous acid (100 mL, 1.4 mol dm3) andhydroquinone (50 mL, 2.2 mol dm3). Both solutions were prepared bydissolving the respective compounds in deionized water.

Hydroquinone was heated at 65° C. with stirring and after maintainingthe selenous acid 65° C. for 10 min, the selenous acid was added quicklyto the hydroquinone. While holding the temperature at 65° C., thestirring was continued for 30 more minutes to ensure the completereduction of selenium.

b. Adsorption of NanoSe on Sponge

1. Sponge was weighed (0.37 g), washed with nanopure water and dried inoven at 110° C. for 30 min.

2. It was then soaked in 25% sucrose solution for 15 min,

3. The sponge was squeezed to remove excess sucrose.

4. Sponge was soaked in as prepared NanoSe solution from the procedurementioned above for 15 min.

5. Sponge was then taken out and squeezed and put in oven for drying

6. After drying, the sponge was washed many times with large quantitiesof nanopure water until no leaking of NanoSe was observed in water.

7. Sponge was dried in oven and used to test mercury capture efficiency.

c. Sponge-Supported Growth of NanoSe

Commercially available sponge (0.37 g) was treated as follows:

Method #1

1. Sponge was washed with nanopure water and dried in oven at 110° C.for 30 min.

2. It was soaked in 25% sucrose solution for 15 min,

3. Then it was taken out and squeezed to remove excess sucrose.

4. Sponge was soaked in selenous acid for 30 min.

5. When hydroquinone, for synthesis of NanoSe was ready, this spongealong with rest of solution was put into this solution. After thatsynthesis procedure was followed till end.

6. Sponge was taken out and squeezed and put in oven for drying

7. After that it was washed many times with large nanopure water untilno leaking of NanoSe was seen in water.

8. The sponge was dried in oven and used for testing mercury captureefficiency.

Method #2

1. Sponge was washed with nanopure water and dried in oven at 110° C.for 30 min.

2. It was soaked in 25% sucrose solution for 15 min,

3. Then it was taken out and squeezed to remove excess sucrose.

4. Sponge was soaked in selenous acid for 30 min.

5. Then sponge was taken out without squeezing and put in oven to dry.

6. Once dry, the sponge was immersed in hydroquinone solution and heatedfor 10 min at 65° C.

7. Then, more selenous acid was added to the mixture to allow NanoSesynthesis

8. Sponge was taken out and squeezed and put in oven for drying

9. After that it was washed many times with nanopure water until noleaking of NanoSe was seen in water.

10. The sponge was dried in oven and used for testing mercury captureefficiency.

Method #3

1. Sponge was washed with nanopure water and dried in oven at 110° C.for 30 min.

2. It was soaked in 25% sucrose solution for 15 min,

3. Then it was taken out squeezed to remove excess sucrose.

4. Sponge was soaked in selenous acid for 15 min.

5. Hydroquinone solution is heated at 65° C. for 10 min, then the spongealong with the rest of selenous acid solution was added to the heatedhydroquinone solution. When solution turns orange (approximately after15 min), the beaker was placed on ice immediately and left for 30 min tostop the reaction.

6. After that, the sponge was taken out and squeezed to remove excessselenous acid, put in oven at 110° C. until it turns brown(approximately after 30 min).

7. It was washed many times with nanopure water until no leaking ofNanoSe was seen in water.

8. The sponge was dried in oven and used for testing mercury captureefficiency.

Method #4

9. Sponge was washed with nanopure water and dried in oven at 110° C.for 30 min.

10. It was soaked in 25% sucrose solution for 15 min,

11. Then it was taken out squeezed to remove excess sucrose.

12. Sponge was soaked in selenous acid for 15 min.

13. Hydroquinone solution is heated at 65° C. for 10 min, then thesponge was squeezed and released to uptake hydroquinone. Sponge wastaken out and put in oven at 110° C. After 30 min, 1 mL of selenous acidwas added to the sponge and it was squeezed and released to uptakesolution and then left in oven for 1.30 h.

14. After that, the sponge was taken out and squeezed to remove excessselenous acid and then put in oven at 110° C. for 30 min (until itdries)

15. It was washed many times with nanopure water until no leaking ofNanoSe was seen in water.

16. The sponge was dried in oven and used for testing mercury captureefficiency.

d. Mercury Removal Efficiency Using NanoSe Materials Grown withDifferent Methods

Mercuric ion removal efficiency was verified by preparing 7-8 ppmsolution of HgCl₂. The sponges were then soaked in the Hg solution(volume equivalent to uptake capacity of sponge) for 30 min. The waterwas retrieved by squeezing, and then analyzed for mercury content at theSoil Testing Lab at the University of Minnesota. The results are shownin Table 1.

Results: The results showed that selenium adsorbed and as well as grownon sponge was very efficient in removing mercury (Hg). Even with veryhigh concentration of Hg, total mercury was detected in parts perbillion (ppb) which is well below the EPA limit for drinking water (2ppb) and fish contamination. Although all the different treatments thatwere done on the sponges showed results in ppb, the sponge which wastreated with Method #2 showed impressive results by decreasing mercurycontent from 8 ppm to 0.0046 pm (Table 1), which corresponds to 99.95%removal efficiency, higher than the state of the art mercuryadsorbents.[9, 10] The SEM images also showed that the sponge treatedwith method #3 and #4 exhibits better control on particle size(monodispersity), coverage and distribution on the surface of the spongeas compared to other methods (FIGS. 1, 2 and 3).

TABLE 1 Efficiency of mercury removal by NanoSe sponge prepared withdifferent methods Total mercury in (ppm) left in water Sponge aftertreating with NanoSe sponge. treatment (original Hg concentration: 8ppm) Adsorbed 0.76 NanoSe Method #1 1.02 Method #2 0.0046 Method #3 0.18Method #4 0.33

IV. Market of Mercury Removal

5.1. Current Needs

-   -   Mercury removal from water        -   Mercury capture from rain water using wetlands (EPA)        -   Mercury removal from water in the mining and petroleum            industries        -   Mercury removal from surface waters such as lakes and rivers            (currently not done because of lack of suitable            technological solutions)        -   Mercury removal in waste water treatment plants    -   Mercury removal from gas emissions        -   Coal-fired plants: In the US only, they are over 1,100            coal-fired plants, which emit around 48 tons of mercury per            year.        -   Cement industry, petroleum and gas industries

III. Methods for Chemical Synthesis of Colloidal Selenium Nanospheres

1. State of the Art and Novelty

A number of companies including Sigma-Aldrich, American Elements andNanocs commercialize selenium nanoparticles with a diameter <200 nm(limited size).

So far, the only method that provide good quality selenium nanospheresup to 500 nm diameter uses bacteria and other microorganisms thatproduce the nanospheres after a few days of cell culture.[17, 18]. Apatent on the bacterial process was published in 2010. [19]. Here wereport a simple, rapid and cheap chemical method that produces perfectlyspherical nanospheres (50-500 nm) in less than an hour.

2. Technology Description

The use of method #3 to grow nanoselenium on a natural honeycomb spongeleads to the synthesis of monodisperse and perfectly spherical seleniumnanospheres (SeNS) (FIG. 4). The same nanospheres can be grown on othersponges or materials by modifying the surface tension and control theinterface forces of the material. The SeNP can be retrieved in solutionto obtain colloidal SeNP by using one of the 3 methods:

-   -   Sonicating the sponge in the presence of a surfactant    -   Coating the sponge with a hydrosoluble or thermosoluble film        before the growth of nanoselenium particles.    -   Dissolve the cellulose composing the sponge to release the        nanoparticles

3. Applications:

Recent reports revealed that selenium nanoparticles have a number ofuseful properties including:

-   -   Optoelectric properties (converting light into electricity),[20]        which could be useful in the fabrication of solar cells,        photosensor detectors and photocopiers    -   Antimicrobial properties, which can have applications in coating        medical devices or surfaces.[21, 22]    -   Bioprotective activity, such as nephroprotection [23].    -   Antitumoral activity, which could be used for cancer treatment        by inducing apoptosis in tumor cells[24]

REFERENCES

-   1. Zhang, H., et al., Selenium in Soil Inhibits Mercury Uptake and    Translocation in Rice (Oryza sativa L.). Environmental Science &    Technology, 2012. 46(18): p. 10040-10046.-   2. Monson, B. and S. Heiskary, Water Mercury Concentrations in    Minnesota Lakes. 2008, Minnesota Pollution Control Agency.-   3. McCann, P., Mercury Levels in Blood from Newborns in the Lake    Superior Basin 2011, Minnesota Department of Health-   4. Agency, U.S.E.P., Treatment Technologies for Mercury in Soil,    Waste, and Water 2007.-   5. Mattigod S V, G. F., and K E Parker, A Thiol-functionalized    Nanoporous Silica Sorbent for Removal of Mercury from Actual    Industrial Waste, in Environmental Applications of Nonomaterials:    Synthesis, Sorbents and Sensors. 2007. p. 275-283.-   6. Liu, T., et al., Alkenyl/Thiol-Derived Metal-Organic Frameworks    (MOFs) by Means of Postsynthetic Modification for Effective Mercury    Adsorption. Chemistry—A European Journal, 2014. 20(43): p.    14090-14095.-   7. Samiey, B., C.-H. Cheng, and J. Wu, Organic-Inorganic Hybrid    Polymers as Adsorbents for Removal of Heavy Metal Ions from    Solutions: A Review. Materials, 2014. 7(2): p. 673-726.-   8. Sohrabi, M., Preconcentration of mercury(II) using a    thiol-functionalized metal-organic framework nanocomposite as a    sorbent. Microchimica Acta, 2014. 181(3-4): p. 435-444.-   9. Yee, K.-K., et al., Effective Mercury Sorption by Thiol-Laced    Metal-Organic Frameworks: in Strong Acid and the Vapor Phase.    Journal of the American Chemical Society, 2013. 135(21): p.    7795-7798.-   10. Li, B., et al., Mercury nano-trap for effective and efficient    removal of mercury(II) from aqueous solution. Nat Commun, 2014. 5.-   11. Khan, M. A. K. and F. Wang, Mercury-selenium compounds and their    toxicological significance: Toward a molecular understanding of the    mercury-selenium antagonism. Environmental Toxicology and    Chemistry, 2009. 28(8): p. 1567-1577.-   12. Johnson, N.C., et al., Mercury Vapor Release from Broken Compact    Fluorescent Lamps and In Situ Capture by New Nanomaterial Sorbents.    Environmental Science & Technology, 2008. 42(15): p. 5772-5778.-   13. Hurt, R. H., et al., Nanostructured sorbent materials for    capturing environmental mercury vapor. 2013, Google Patents.-   14. Ajeet Kumar, I. S., Dan V. Goia, Synthesis of selenium particles    with various morphologies. Journal of Colloid and Interface    Science, 2006. 416: p. 119-123.-   15. Sawyer, J., Mercury removal from water. 2012, Google Patents.-   16. Lee, K., Nanosorbents and methods of use thereof. 2012, Google    Patents.-   17. Debieux, C. M., et al., A bacterial process for selenium    nanosphere assembly. Proceedings of the National Academy of    Sciences, 2011. 108(33): p. 13480-13485.-   18. Oremland, R. S., et al., Structural and Spectral Features of    Selenium Nanospheres Produced by Se-Respiring Bacteria. Applied and    Environmental Microbiology, 2004. 70(1): p. 52-60.-   19. Prokisch, J. and M. A. Zommara, Process for producing elemental    selenium nanospheres. 2010, Google Patents.-   20. Dong, H., et al., Colloidally stable selenium@copper selenide    core@shell nanoparticles as selenium source for manufacturing of    copper-indium-selenide solar cells. Journal of Colloid and Interface    Science, 2014. 415(0): p. 103-110.-   21. Tran, P. A. and T J. Webster, Antimicrobial selenium    nanoparticle coatings on polymeric medical devices.    Nanotechnology, 2013. 24(15): p. 155101.-   22. Wang, Q. and T. J. Webster, Nanostructured selenium for    preventing biofilm formation on polycarbonate medical devices.    Journal of Biomedical Materials Research Part A, 2012. 100A(12): p.    3205-3210.-   23. Li, Y., et al., Functionalized selenium nonoparticles with    nephroprotective activity, the important roles of ROS-mediated    signaling pathways. Journal of Materials Chemistry B, 2013.    1(46): p. 6365-6372.-   24. Huang, Y., et al., Selective cellular uptake and induction of    apoptosis of cancer-targeted selenium nanoparticles.    Biomaterials, 2013. 34(29): p. 7106-7116.

Example 2

Images illustrating the contact angles of the sponges described in Table2 are shown in FIG. 5. Results of the Fourier transform infraredspectroscopy (FTIR) analysis of the sponges are shown in FIG. 6 and FIG.7.

TABLE 2 Characterization of the sponges. Average Chemical ContactComposition Sponge Angle (Spectroscopic type (degree) analysis by FTIR)Application/Product Synthetic 140 ± 5 Polyurethane (PU)Nanoselenium-coated sponge (highly and its derivatives sponge as filtersfor (Sponge hydro- mercury capture PU) phobic) Natural  77 ± 5 Polyamide(PA) and Synthesis and storage of Honeycomb (Hydro- its derivativescolloidal selenium sponge philic) nanospheres with a (Sponge diameterrange of 100 nm PA) to 1 micrometer)

Example 3

This example demonstrates that a selenium nanomaterial can grow on agold surface, that is, a substrate without hydroxyl (—OH) groups, or asilicon surface.

In a modification of Method #3 of Example 1, a selenium nanofilm wasformed on a gold surface by placing gold-coated glass in a 1.4 Mselenous acid (SA) solution for 15 minutes, then exposing the surface to0.7 M a hydroquinone solution for 10 minutes. Growth was stopped byplacing the surface on ice when the hydroquinone solution turned orange.A photograph of a representative nanofilm is shown in FIG. 8, andscanning electron microscopy (SEM) images are shown in FIG. 9.

In a modification of Method #7, described below, gold-coated glass wasplaced in a 25% sucrose solution for 15 minutes. Gold-coated glass wasthen placed in a 1.4 M SA solution for 30 minutes. The plate was driedin oven at 110° C. for 15 minutes. The plate was then placed in a 0.7 MHQ solution for 10 minutes. More selenous acid (0.7 M) was added afterexposure to HQ and the sponge was treated for an additional 20 minutes.The sponge was then dried in an oven at 100° C. until dry, usually 30 to45 minutes. The resulting films are shown in FIG. 10 and FIG. 11.

In a modification of Method #7, described below, a selenium nanofilm wasformed on a silicon surface. Results are shown in FIG. 12.

Method #7: A natural honeycomb sponge was first coated with sucrose. Thesponge was then put in a 1.4 M selenous acid solution for 30 minutesbefore being dried in an oven without squeezing at 110° C. The spongewas then added to a hydroquinone (HQ) solution (at differentconcentrations between 0.1M and 5.5M) for 10 minutes. More selenous acidwas added to the sponge after exposure to HQ. A wide range ofnanospheres sizes (e.g., 50 nm to 1000 nm) can be obtained by alteringthe concentration of hydroquinone, as shown in FIG. 13.

Nanospheres synthesized on a natural honeycomb sponge using Method #7can be retrieved from the sponge by washing with water, as shown inschematic form in FIG. 14.

Example 4 Antimicrobial Activity of Selenium Nanomaterials:

A sensitivity test was performed to evaluate the antimicrobialproperties of a nanoselenium-coated sponge using E. coli bacteria. Ahigh anti-microbial activity was observed, as demonstrated by theappearance of an inhibition zone, as shown in FIG. 15.

Example 5

Described is a novel approach for rapid synthesis and long-termpreservation of selenium nanospheres (SeNS) on a solid microporoussupport by combining a mild hydrothermal process with chemicalreduction. By using a natural sponge as a solid 3-dimensional matrix fornanoparticle growth, highly monodisperse spherical nanoparticles can besynthesized with a wide size range (10 nm to 1000 nm) and extremely highyield in a relatively short period of time (1 hour). Additionally, thesynthesized SeNS can be stored and retrieved as needed by washing thesponge in water. Keeping the nanospheres in the support offersremarkable long-term stability because particles left on the spongepreserve their morphological and colloidal characteristics even after 8months of storage. Furthermore, the selenium nanospheres can be used forefficient mercury capture from contaminated waters with arecord-breaking mercury removal capacity of up to 1900 mg/g.

Results and Discussion

The need for a stabilizing agent provides main limitation ofsynthesizing colloidal nanoparticles in the liquid phase when in thesubsequent long-term stability of the nanoparticles in solution. The useof a sponge provides a means to overcome these limitations and providesincreased surface to volume ratio for nanoparticle growth, thusincreasing the yield. Also, the sponges offer a confined environment tofacilitate diffusion and enhance chemical interactions. Furthermore, thesponge can be used not only for nanoparticle growth but also forlong-term storage. Such advantages overcome the need for nanoparticlepreservation through daunting and costly lyophilization processes(Alkilany et al. Langmuir, 2014, 30, 13799-13808; Abdelwahed, et al.,Advanced Drug Delivery Reviews, 2006, 58, 1688-1713) or nanoparticlestorage in solutions prone to changes in pH and unstable aqueousenvironments (Fang et al. Small (Weinheim an der Bergstrasse, Germany),2009, 5, 1637-1641).

Sponge-Supported Synthesis. The first challenge in this work was to finda sponge with a suitable interface that can adsorb selenous acid andallow nanoparticle growth, while offering a weak interaction with thenanoparticles to allow easy retrieval of the nanoparticles in solution.To favor isotropic nanoparticle growth on the sponge fibers and not insolution, a process that follows two major phases was designed: (1)immobilization of selenous acid on the sponge fibers, and (2)nanoparticle growth on the sponge surface. The immobilization isperformed by immersion of the sponge in a 25% sucrose solution. Thesponge is then squeezed before being immersed in selenous acid solutionand dried in a vacuum oven for 10 minutes at 110° C. These steps providea homogeneous sucrose coating on the sponge to allow isotropicimmobilization of the selenous acid ions by interaction with the sucrosehydroxyl groups, thus promoting a homogenous growth of nanoparticles.The drying step is intended to remove excess liquid from the sponge andinduce the attachment of the sucrose-Se ions into the sponge fibers.After drying, the sponge is immersed in a reducing agent solution suchas hydroquinone to convert the adsorbed Se ions into elemental selenium(Se⁰). Further immersion of the sponge in additional Se ions solutionleads to SeNS surface growth on the sponge fibers.

Sponge Properties. To select an adequate sponge, the synthesis processwas conducted on a number of synthetic and natural sponges includingpolyvinyl alcohol (PVA), polyurethane (PU), silk (composed of fibroinproteins) and honeycomb (composed of spongin scleroproteins) sponges.Scanning electron microscopy (SEM) images showed that PVA, PU, and silksponges performed poorly (Supporting Information, FIG. 16). Aftersynthesis, all sponges changed color to dark brown indicating the growthof nanoparticles. While the PVA sponge showed small nanoparticles withlow density, PU and silk sponges showed aggregates. In addition,harvesting the particles from the sponges was unsuccessful due to astrong adsorption to the sponge fibers but also due to low thermalstability of PVA and silk sponges during the hydrothermal process at110° C. The honeycomb sponge revealed remarkable growth of perfectlyspherical nanoparticles (FIG. 17). The SEM images (FIGS. 17a and 17b )showed that the sponge fibers were completely and densely covered withmonodisperse nanospheres. A simple washing of the sponge with roomtemperature water resulted in an instantaneous release of most of thenanoparticles into solution with very low amount of sucrose fibers (FIG.17c ). The yield and quality of SeNS can be explained by a combinationof morphological, chemical and interfacial properties of the honeycombsponge but also by the growth mechanism discussed later. Unlike the PVA,PU and silk sponges that all have water contact angles higher than 110°,the honeycomb sponge composed mainly of polyamide shows a hydrophilicsurface with a contact angle of 77°±5° (FIG. 18). This hydrophilicityfavors the interaction of sucrose and selenous acid with the spongefibers through intermolecular hydrogen bonds (O—H . . . Se), andprevents the aggregation of nanoparticles as observed with othersponges. In addition to the interfacial properties, the polyamidecomposition of honeycomb sponge offers a high heat and chemicalresistance and good mechanical properties. The yield of SeNS isparticularly remarkable and could be explained by the multiple growthmechanisms that will be addressed in the following sections, as well asthe 3D matrix of the sponge. The sponge fibers (10 μm to 30 μm indiameter and 10 nm to 20 nm in surface roughness) provide a high surfaceto volume ratio, which is of importance as the nanoparticle growthmechanism can depend on surface diffusion. Also, the hydrophilicity ofthe sponge allows absorption of up to 20±3 mL water/g sponge.

Role of Sucrose. Sucrose was used to provide a uniform surface for theinitial reduction of selenium. To gauge the effect of other saccharidesand the impacts of both monosaccharides and disaccharides, the synthesiswas conducted with four different sugars: fructose, glucose, lactose andsucrose. Only treatment with fructose resulted in particle growth withsimilar quality than sucrose, with regard to particle size,monodispersity and surface coverage (FIG. 19). Lactose and glucoseyielded fused, non-spherical particles. These results along with thecomposition of sucrose (a combination of a fructose and glucose units),and lactose (a combination of a glucose and galactose units) couldsuggest that the efficiency of sucrose in this process may be due to itsfructose unit. An additional experiment was conducted to ascertain theproper level of sucrose loading. Briefly, sponges soaked in varyingsucrose concentrations (5%, 10%, 25%, and 50%) were used in thesynthesis described above, and the sponges analyzed with SEM imaging.The results depicted in FIG. 20 indicate that a sucrose concentration of5% is sufficient to provide the optimum growth condition for SeNS, andthe increase in sucrose concentration up to 25% does not affect thequality of the nanoparticles. However, nanoparticle retrieval seems tobe easier at a concentration of 25% sucrose. Without any saccharidecoating, SeNS appeared in non-uniform patches with a poor yield, highpolydispersity, and significant agglomeration.

Growth Mechanism and Size Control of SeNS. In the process of thisExample, SeNS synthesis involves two major steps: an initialhydrothermal growth, followed by growth through chemical reduction usinghydroquinone. FIG. 21a shows the composition of the growth medium duringthe combined hydrothermal/chemical reduction process. Three types ofnanoparticles can be distinguished: (i) a highly dense network of smallSeNS of 5-10 nm, (ii) medium-size SeNS or 50-150 nm, and largerparticles of 200-1000 nm. When the sponge is observed after thehydrothermal process and without chemical reduction, only small andmedium-size particles are found. FIG. 21 (b 1-d) also reveals that thesmall SeNS are crystalline (d(021)=0.301 nm), while all other particlesin the medium are amorphous. This result is also confirmed by Ramananalysis (FIG. 22). Another unexpected result is shown in FIG. 21 (d 1and d2). The small crystalline SeNS seem to be internalized by themedium-size particles, which represent the first hint of one of thegrowth mechanisms. The energy dispersive X-ray (EDX) spectrumdemonstrates that all nanoparticles are solely composed of pure selenium(FIG. 21f ). The observed copper and trace carbon and silicon are causedby the TEM grid.

The composition of the growth medium provides some insight into thegrowth mechanism where surface diffusion of different growth speciesplays a role. When the selenous acid soaked sponge is heated, theselenium ions present in the sponge matrix are reduced to elementalselenium (Se⁰). The reduction is believed to be primarily caused by theheating, the mild vacuum conditions were used in this synthesis toexpedite evaporation of water from the sponge. The reduced selenium ionsthen diffuse and crystalize on the surface of the sponge fibers underthe effect of heat (110° C.) and rapid water evaporation. The surfacediffusion results in instantaneous growth of 5 nm to 10 nm crystallineSeNS. The small crystalline SeNS reach a maximum size of 10 nm to 15 nm,probably due to diffusion-limited growth. The second set of SeNSobserved after the hydrothermal process are around 50 nm to 150 nm (FIG.23a, b ). These particles grow and reach their maximum size within thefirst 5 minutes of the hydrothermal process. When the sponge isincubated for different times under hydrothermal conditions, theretrieved SeNS solutions exhibit different colors depending on theincubation time (FIG. 23c ). However, the change in color afterdifferent incubation times (5 minutes, 10 minutes, 15 minutes) may bemore indicative of a change in nanoparticle concentration anddistribution rather than nanoparticle size, as shown by SEM images (FIG.24).

As for the amorphous SeNS with a size range of 50 nm to 150 nm, theirgrowth is likely mediated by two concurring mechanisms. First, surfacediffusion of elemental selenium under heating results in amorphousagglomeration due to interfacial forces generated by rapid waterevaporation. The resulting SeNS then continue their growth up to around150 nm by internalizing the small crystalline SeNS that come intocontact due to surface diffusion. FIG. 21 (d, e, f, g) reveal that bothsmall crystalline SeNS and medium-size amorphous particles diffuse andare internalized by bigger “phagosome” nanoparticles. This mechanismcould explain the high monodispersity of the synthesized nanoparticles,as big particles grow by internalizing small ones. A close look at theinternalized small crystalline nanoparticles shows that the particlesare not only internalized but also undergo a phase change fromcrystalline to amorphous within the host particle. FIG. 23 h1-h4represents crystalline SeNS before (h1) and after internalization(h2-h4). Images h1-h4 were taken from nanoparticles localized atdifferent distances from the center of the phagosomal particle.Nanoparticles that are closer to the center are particles that wereinternalized first and thus have a longer residence time inside thephagosomal particle. The high-resolution transmission electronmicroscopy (HRTEM) imaging reveals that the internalization processimmediately affects the crystalline structure by decreasing the fringespacing from d(021)=0.301 nm (FIG. 23 h1) to d(230)=0.201 nm (FIG. 23h2). Over time, the internalized SeNS become amorphous and cannot bedistinguished from the surrounding material.

Once the sponge is removed from the vacuum oven (hydrothermal process),the sponge contains mainly small crystalline SeNS and medium-sizeamorphous SeNS. To allow further growth of the nanoparticles, the spongeis immersed in hydroquinone as a reducing agent, then exposed to asolution of selenous acid. The chemical reduction promotes furtherbinding to the nanoparticles present on the sponge. From this point,SeNS growth on the sponge fibers likely occurs via two main reactionpathways (FIG. 25). Selenium ions present in solution can be reduced atthe vicinity of the sponge surface and either diffuse and condense onalready grown nanoparticles on the surface, or agglomerate in solutioninto small amorphous particles that will be internalized once they reachthe surface. Concurrently, large SeNS can grow by surfacediffusion/internalization of medium-size nanoparticles as describedearlier. These reaction pathways are non-exclusive, as particles canform via one or many of these processes simultaneously. The chemicalreduction not only allows further growth of SeNS but also enables sizecontrol from 100 nm to 1000 nm by varying hydroquinone concentration(FIG. 26). This size control can allow control of catalytic, biologicaland optical properties of nanoparticles dependent on their size.Increasing the concentration of HQ in solution resulted in greaterreduction and consequently, larger particles on the surface of thesponge. It should be noted that the relationship between HQconcentration and SeNS size is linear with an R²=0.93. At concentrationsabove 3 M, however, the polydispersity index increases slightly. Asimple centrifugation or filtration can easily separate the bigparticles from the rest (FIG. 27). When concentrations at 3 M and aboveare not considered the statistical correlation improves slightly(R²=0.97). This correlation is obtained at an optimum of pH 1.6 for thegrowth medium. The increase in pH dramatically affects nanoparticlegrowth and results in low surface coverage (FIG. 28). Since thereduction of selenous acid into elemental selenium also occurs duringthe hydrothermal process, the effect of temperature on the growth andsize of SeNS was investigated. The SEM images reveal that temperaturesof 110-120° C. represent the optimum conditions for the synthesis ofSeNS smaller than 150 nm, without any chemical reduction. A decrease intemperature to 90° C. results in the formation of fused nanospheres,while an increase in temperature leads to an increase in nanoparticlesize but also in a significant increase in polydispersity (FIG. 29).

Long-Term Stability of SeNS. One of the major benefits of thesponge-supported synthesis described herein compared to the methodsshown in Table 3 is that particles can be harvested from the supportwhenever needed by simple washing with water. Sucrose also promotesstability of the harvested particles as it enters into solution when theparticles are retrieved from the sponge. To assess the long-termstability of the SeNS when stored on the sponge, SeNS solution obtainedfrom the sponge immediately after synthesis was compared with a SeNSsolution obtained from a sponge stored for 8 months (Table 4). Theresults show that the nanoparticles stored in the sponge for 8 monthsare remarkably preserved with no change to their size, zeta potentialand polydispersity index. The nanoparticle retrieved immediately aftersynthesis show significant changes in all parameters with noticeablenanoparticle aggregation after 3 months of storage in solution. Moredramatic changes and nanoparticle aggregation are observed for thecommercial SeNS after only 1.5 month of storage in solution (FIG. 30).

TABLE 3 Comparison of different synthesis methods of seleniumnanospheres Sponge- Solution- Microbial- Hydro- Irradiation- supportedphase mediated thermal assisted synthesis (this Parameter synthesissynthesis synthesis synthesis Example) Process time 2 h 12-24 h N/A 30min 1 h Diameter (nm) 5-300 nm 1-500 nm 10-20 nm 5-120 nm 10-1000 nm PDIMono- Poly Mono- Poly Mono- disperse disperse disperse disperse disperseZeta potential −59 to +59 mV −25 to +25 mV — — +25 mV Long term 1 day to3 Not Not Not >8 months on stability at months Published PublishedPublished the sponge room temperature Structure Mostly Crystalline,Crystalline NA Crystalline, amorphous amorphous amorphous

-   Solution-phase synthesis: Gates et al., Advanced Functional    Materials, 2002, 12, 219-227.; Jeong et al., Advanced Materials,    2005, 17, 102-106; Nie et al., Journal of Materials Chemistry B,    2016, 4, 2351-2358; Chen et al., Crystal Growth & Design, 2009, 9,    1327-1333; Kumar et al., Journal of Colloid and Interface Science,    2014, 416, 119-123; Stroyuk et al., Colloids and Surfaces A:    Physicochemical and Engineering Aspects, 2008, 320, 169-174; Shah et    al., Nanotechnology, 2007, 18, 385607; Zhang et al., Langmuir, 2010,    26, 17617-17623.-   Microbial-mediated synthesis: Oremland et al., Applied and    Environmental Microbiology, 2004, 70, 52-60; Shirsat et al., RSC    Advances, 2015, 5, 92799-92811; Jain et al., Environmental Science &    Technology, 2015, 49, 1713-1720-   Hydrothermal synthesis: Shin et al., Materials Letters, 2007, 61,    4297-4300.-   Irradiation-assisted synthesis: Yu et al., New Journal of Chemistry,    2016, 40, 1118-1123.

TABLE 4 Comparison of the long-term stability of SeNS after 8 months ofstorage in the sponge (Sample B) or in solution (Sample C) at roomtemperature as compared to Sample A (as synthesized SeNS). The resultsare also compared to the stability of a commercial SeNS solution. SampleA Sample B Sample C As After 8 After 3 Commercial SeNS synthesizedmonths in months in As After 1.5 in the sponge the sponge solutionpurchased months Size 277 ± 20 291 ± 26 3,260 (50%) 565 ± 111 (6%) 548 ±191 (63%) (nm) (100%) (96%)   907 (50%) 2,079 ± 768 (14% ± 7) 4,100 ±2,000 (35%) 139 ± 25 (50%) 126 ± 1 (2%) 16 ± 1 (29%) Zeta 24 ± 2 26 ± 1−17 ± 3 −42 ± 1 88 ± 2 potential PDI 1.04 1.17 7.10 — —

Selenium Nanospheres as Mercury Sorbent. One of the major properties ofselenium is its strong interaction and affinity to mercury. To evaluatethe ability of selenium nanospheres to sequestrate mercury from water,SeNS solution was mixed with a solution of mercury ions (Hg²⁺) withdifferent concentrations. The mercury adsorption isotherm showed in FIG.31 indicates that the adsorption follows a Langmuir model with R² equalto 0.94. The adsorbate maximum load or maximum removal capacity of SeNS(Q_(e)) at equilibrium was calculated from Equation 1.

$\begin{matrix}{Q_{e} = {\frac{C_{i} - C_{f}}{m} \times V}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

where C_(i) is the initial concentration of mercury ions in the solution(mg/L), C_(f) is the final concentration of mercury ions in the solution(mg/L), m is the mass of adsorbent (g/L), V is the volume of thesolution (L), and Q_(e) is the amount of metal ion adsorbed in gram pergram of adsorbent at equilibrium (g/g).

The maximum removal capacity (Q_(e)) was found to be 1.907 g/g or 1907mg/g. This value is two times higher than the best results reported formetal-organic frameworks for mercury capture (Zhang et al., Nat.Commun., 2014, 5:5537). In addition, this value means that 74.8% ofselenium atoms interact with mercury (the maximum theoretical load ofmercury with a 1:1 stoichiometry is 2540 mg of mercury per gram ofselenium), which is a 7-fold improvement as compared to the performancereported in literature for selenium nanoparticles (Johnson et al.Environmental Science & Technology, 2008, 42, 5772-5778).

The favorability of the interaction between mercury and seleniumnanospheres was evaluated by calculating the separation factor (R_(L))as indicated in Equation 2.

$\begin{matrix}{R_{L} = \frac{1}{1 + {K_{L} \cdot C_{o}}}} & {{Equation}\mspace{11mu} 2}\end{matrix}$

where the parameter K_(L) is the Langmuir adsorption constantcorresponding to the inverse of the intercept in the linear plot in FIG.5, and C_(o) refers to initial concentration of adsorbate.

The value of 0<R_(L) was found to be equal to 0.3, which indicates ahighly favorable interaction (0<R_(L)<1).

Materials and Methods

All chemicals including selenous acid (98%), sucrose (>99.5%), lactose(>99%), fructose (>99%), glucose (>99.5%) and hydroquinone (99%) werepurchased from Sigma Aldrich (St. Louis, Mo., USA). Natural, unbleachedhoneycomb sponges (5-6 in), polyvinyl alcohol sponges, and natural silksponges were purchased from various online suppliers. All aqueoussolutions were prepared in nanopure water.

Characterization of natural honeycomb sponge. The natural sea sponge wascharacterized using scanning electron microscopy (JEOL 6500, 6700 SEM)and Fourier transform infrared spectroscopy (Nicolet Series II MagnaIR-System FTIR, Thermo Fisher Scientific, Waltham, Mass.). Averagesurface roughness and microscopic contact angle were measured using aKLA-Tencor P-7 and an MCA-3 (Kyowa Interface Science Co., Japan)respectively. Absorption capacity was estimated via water uptake insponges of uniform size.

Synthesis of Selenium nanospheres on natural honeycomb sponge. A naturalsea sponge was first soaked in 25% sucrose in nanopure water for 15minutes. The sponge was then submerged in a selenous acid solution (1.4M) for 25 minutes. After removal of the sponge the remaining solutionwas stored at room temperature and used later in the synthesis process.The soaked sponge was then carefully removed and dried in a vacuum oven(−2.6 kPa) at 110° C. (Isotemp vacuum oven Model 280A, Thermo Fisher,Scientific, Waltham, Mass.) for 10 minutes. After drying, the sponge wasadded to a hydroquinone solution (at different concentrations dependingon the desired nanosphere size) for 10 minutes. The remaining selenousacid from the previous step was added to the sponge after exposure tohydroquinone. The sponge was then washed with nanopure water to retrievethe selenium nanospheres for further characterization or use.

Nanoparticle characterization. Selenium nanoparticles were recoveredfrom the sponge via washing in water and used for characterization.Smaller particles were drop casted onto silicon wafers directly fromsolution. Larger particle solutions were centrifuged (14000 rpm for 10minutes) and suspended in fresh nanopure water prior to drop casting.Scanning electron microscopy (SEM) imaging was performed using JEOL6500. Dynamic light scattering (DLS) was conducted using a MicrotracNanoFlex particle analyzer to determine the size, zeta potential andpolydispersity index of the recovered nanospheres solution. Energydispersive X-ray analysis (EDXA) and high resolution transmissionelectron microscopy (HRTEM) were conducted using a FEI Tecnai G² F30electron microscope (Thermo Fisher, Scientific, Waltham, Mass.). Samplesfor TEM imaging were prepared by drop-casting 3 μL sample on a carboncopper grid (Carbon square mesh, CU, 200 mesh from Electron MicroscopySciences, Hatfield, Pa.). Raman spectroscopy was performed using anAlpha300R confocal Raman microscope (WITec Instruments Corp., Knoxville,Tenn.) with a UHTS300 spectrometer and a DV401 CCD detector with anOmnichrome Argon ion laser with 532 nm excitation and 50 mW output powerwas used. For Raman sample preparation, nanoparticles were centrifugedat 12,000 rpm for 30 minutes and the pellet was re-suspended in water.Then 20 μL was drop casted on a Si substrate and dried at roomtemperature for subsequent analysis.

Nanoparticle filtration. The separation of micrometric SeNS from smallerSeNS (FIG. 24) was performed by membrane filtration. After recovery ofSeNS from the sponge via washing in water, solutions were passed through0.4 μm polycarbonate filter membranes (WHATMAN Nucleopore Track-EtchMembrane) using an extrusion device (Mini-Extruder Set, Avanti PolarLipids Inc., Alabaster, Ala.).

In this work, a novel method of SeNS synthesis on a porous solid supportis presented. Different natural and synthetic sponges with differentsaccharide coatings have been studied as 3-dimensional supports to hostnanoparticle growth. By using a sucrose-coated natural honeycomb sponge,monodisperse selenium nanospheres with a wide size range (0.01 μm to 1μm) and remarkable yield have been successfully synthesized. Inaddition, the synthesized SeNS can be harvested whenever needed bywashing the sponge in water, without any loss or change in nanoparticlesize, zeta potential, or monodispersity. Furthermore, scanning andtransmission electron microscopy imaging revealed the growth of SeNSwith a number of different mechanisms that have not been previouslyreported including nanoparticle protuberance and nanoparticleinternalization where large particles grow by incorporating smallerones.

Example 6

At the time of the invention, selective removal of aqueous mercury tolevels below 10 nanograms per liter (ng·L⁻¹) or part per trillion (ppt)remained an elusive target for public health and environmental agencies.This example shows that new levels of selective mercury removal can bereached using a rapid and cost-effective technology.

A store-bought polyurethane sponge was used as a 3D matrix to growselenium (Se) nanomaterials on the surface and in the bulk of the spongefibers. The nanoselenium sponge exhibits a record breaking-mercury ions(Hg²⁺) removal rate, regardless of the pH. The exposure of aqueoussolutions containing 10 parts per million (ppm) to 1 parts per billion(ppb) Hg²⁺ to the sponge results in clean water with mercury levelsundetectable by the state of the art analytical methods (detection limit<0.2 parts per trillion (ppt)). Such performance is not only far belowthe acceptable limits in drinking water standards (2 micrograms perliter (μg·L⁻¹) or 2 ppb) and industrial effluents (0.2 ppb), but alsosurpasses the most stringent surface water quality standards (1.3 ppt).The sponge shows unique selectivity towards Hg, does not retain anywater nutrients, and can significantly reduce the concentration of zinc,copper and nickel. Furthermore, the sponge shows no cytotoxic effect onmammalian cells while exhibiting strong anti-microbial properties. Thehigh affinity of Hg for Se results in irreversible sequestration ofmercury by the sponge, yielding a biologically inert and non-toxic Se—Hgcomplex. Leaching experiments show no significant desorption, confirmingthe suitability for landfill disposal.

Growing selenium nanomaterials directly onto and inside a polyurethanesponge by a combined hydrothermal reduction and wet chemical synthesisyields mercury sorbent only overcomes the limitations of the existingselenium nanomaterials at the time of the invention. To evaluate thesponge performance and understand the mode of mercury adsorption, theadsorption kinetics and isotherms were analyzed and the selectivity tomercury and other waterborne elements was investigated. Theanti-microbial properties and the ability to sequestrate other waterpollutants were also studied. The growth of selenium nanomaterials onthe sponge was expected to overcome the need of stabilizing ligands andallow the use of single nanostructures and not aggregates, thusdramatically increasing the surface area for mercury capture. To verifysuch assumption, growing nanostructures were grown with different shapesand sizes and mercury removal experiments were performed. Unexpectedly,the morphology and size of the nanomaterials and thus thesurface-to-volume ratio has no significant effect on the performance.This unexpected result was explained by microscopic and spectroscopicanalysis of the NanoSe sponge. The analysis revealed that seleniumnanomaterials grow not only on the surface of the sponge fibers but alsoin the bulk material, and that mercury undergoes subsurface and bulkdiffusion to interact with both selenium and polyurethane functionalgroups in the whole material, resulting in remarkable removal kineticsand capacity and irreversible mercury binding. Because of the confusionsurrounding the dual health benefits and toxic effects of selenium, thehealth risk was addressed by studying the cytotoxicity of both theNanoSe sponge and the produced Se—Hg complex, and by ensuring that thesponge presents negligible desorption and leaching risk during use.Standard testing protocols were also used to evaluate the non-hazardousnature of the waste sponge and suitability for landfill disposal.

Results and Discussion

Initial experiments to coat a sponge with selenium nanoparticles wereperformed by either soaking the sponge in a pre-synthesized SeNPsolution (dip-coating) or immersing the sponge in the growth solutionduring the synthesis following known protocols (Kumar et al. Journal ofColloid and Interface Science 2014, 416:119-123). As expected, theresults depicted in FIG. 32 show a poor and inhomogeneous coverage ofthe sponge by anisotropic selenium nanoparticles and aggregates.Additionally, the nanoparticles exhibit high desorption from the spongeafter washing.

To avoid these drawbacks, selenium nanostructure was grown directly onthe sponge fibers by soaking the sponge in seleneous acid then drying itat 100° C. to allow both water evaporation and adsorption of theselenium atoms on the sponge as well as their thermal reduction toelemental selenium. The growth can be followed or not by a wet chemistrysynthesis at 65° C. to generate the desired nanostructures includingnanoparticles, nanodomes and nanofilms (FIG. 33). The variety ofmorphologies obtained is likely due to the fact that both thehydrothermal and wet syntheses occur at temperatures higher than theglass transition temperature of amorphous selenium 31±0.5. Attemperatures over 60° C., selenium is in a rubbery state (Su et al.Journal of Materials Research 2010, 25(06):1015-1019), and thedeformation behavior of amorphous selenium near its glass transitiontemperature can lead to amorphous domes or thin nanoselenium layers.

Adsorption kinetics and isotherm. One of the major parameters of mercurysorbents is the contact time which largely defines the adequate flowrate for sample cleaning and the subsequent cost of the process. Theimpact of contact time on Hg²⁺ removal is investigated by immersing thesponge on the mercury solution for a period of time ranging from 1second to 60 minutes (FIG. 34 a, b). The results show that Hg²⁺adsorption can reach an equilibrium state after 1 second for the PUsponge with a maximum removal rate of around 84%. Within the same timeframe (1 second), a NanoSe sponge loaded with 3% w/w selenium removesover 98% of mercury. This rate improves to 99.94% after 15 minutes andreaches 100% (undetectable levels) after 1 hour.

The affinity of the NanoSe sponge for mercury can be evaluated by thedistribution coefficient (K_(d)) defined as:

$\begin{matrix}{K_{d} = {\frac{( {C_{o} - C_{f}} )}{C_{f}} \times \frac{V}{m}}} & {{Equation}\mspace{11mu} 3}\end{matrix}$

where C₀ is the initial Hg²⁺ concentration, C_(f) is the finalequilibrium Hg²⁺ concentration. Since removal rate for NanoSe sponge is100%, the concentration of 0.2 ng·L⁻¹ was taken as C_(f) since itrepresents the limit of detection of the equipment used for mercurydetection. V is the volume of the solution in mL, and m is the mass ofsorbent in g. While the K_(d) value for the PU sponge is relatively low(1.33×10² milliliters per gram (mL·g⁻¹)), the value of K_(d) for NanoSesponge is 1.67×10⁹ mL·g⁻¹, two orders of magnitude higher than the bestvalues reported for Hg²⁺ sorbents so far (Zhang et al. Nat. Commun.2014, 5:5537). Sorbents with K_(d) around 107 mL·g⁻¹ are usuallyconsidered excellent.

The changes in mercury sorption over time exhibit an excellent fit withthe pseudo-second-order kinetic model (Equation 4), with a correlationcoefficient of 0.999 and 1 for the PU and the NanoSe sponge respectively(FIG. 34b ):

$\begin{matrix}{\frac{t}{q_{t}} = {\frac{1}{k_{2}q_{e}^{2}} + \frac{t}{q_{e}}}} & {{Equation}\mspace{11mu} 4}\end{matrix}$

where q_(t) (milligrams per gram (mg·g⁻¹)) is the amount of Hg²⁺adsorbed at time t (minutes (min)), k₂ (grams per milligram per minute(g·mg⁻¹·min⁻¹)) is the rate constant of pseudo-second order adsorption,and q_(e) (mg·g⁻¹) is the amount of adsorbed Hg²⁺ at equilibrium. Therate constants were calculated to be respectively 10.96 g·mg⁻¹·min⁻¹ and713.81 g·mg⁻¹·min⁻¹. The extremely high constant rate for NanoSe spongereveals that the adsorption is two orders of magnitude faster than theone obtained with the state of the art mercury sorbents (Zhang et al.Nat. Commun. 2014, 5:5537).

To determine the adsorption process and the sponge uptake capacity forHg²⁺ ions, adsorption experiments were performed with initial mercuryconcentrations ranging from 10 ppb to 50 ppm using a PU sponge, a NanoSesponge loaded with 3% w/w selenium, and a NanoSe sponge loaded with 50%w/w selenium. (FIG. 34c ). Linear, Langmuir, Freundlich and BETadsorption isotherm models are used to fit the experimental data of Hg²⁺adsorption. The adsorption isotherm was found to follow a Langmuir modelwith a respective correlation coefficient of 0.97, 0.99, and 0.96 forthe PU, NanoSe sponge loaded with 3% w/w selenium, and NanoSe spongeloaded with 50% w/w selenium sponges (FIG. 34d ). The mercury maximumuptake capacity at equilibrium state was calculated from Equation 5.

$\begin{matrix}{q_{e} = {\frac{c_{i} - c_{f}}{m} \times V}} & {{Equation}\mspace{11mu} 5}\end{matrix}$

where q_(e) is the amount of metal ion adsorbed in gram per gram (g·g⁻¹)of adsorbent at equilibrium or maximum uptake capacity, C_(i) is theinitial concentration of Hg²⁺ in the solution (milligrams per liter(mg/L)), C_(f) is the final concentration of Hg²⁺ in the solution(milligrams per liter (mg·L⁻¹)), m is the mass of adsorbent (grams perliter (g·L⁻¹)), V is the volume of the solution (L). The maximum uptakecapacity (q_(e)) was calculated to be respectively 654 mg·g⁻¹ and 624mg·g⁻¹ for the PU and NanoSe sponges, which is higher or similar to thevalues reported in literature. These numbers reveal two points. Thefirst is that despite the slow adsorption, bare PU sponge exhibits amercury uptake capacity. FTIR analysis showed that PU captures mercurythrough interaction with its functional groups, including amine,hydroxyl and carbonyl groups (FIG. 35a ). The FTIR spectra also suggestthat the aromatic groups are involved in this adsorption possiblythrough π-interactions. The second observation is that the modificationof the size or shape of the selenium nanomaterials did not show anynoticeable change in uptake capacity, suggesting that thesurface-to-volume ratio does not play a major role in the uptakecapacity. These results can be explained by the fact that mercury canundergo subsurface penetration and bulk diffusion to populate internalsites. SEM imaging reveals that selenous acid penetrates inside the PUsponge fibers resulting in internal growth of selenium nanoparticles(FIG. 35b ). EDX spectroscopic analysis of a PU fiber cross-sectionconfirmed the presence of selenium inside the material but also revealedthe presence of mercury, thus confirming bulk diffusion of both Se andHg (FIG. 35c ). Mercury bulk diffusion can occur inside the PU fiberseven when they are coated with a NanoSe thin film.

The presence of selenium nanomaterials at a concentration of 3% w/w onthe PU sponge decreases instead of increasing the uptake capacity (FIG.34c ). To further verify this result, a NanoSe sponge with 50% seleniumwas produced and tested. As shown in FIG. 34c , the increase in seleniumload from 3% w/w to 50% w/w results in a significant drop in the mercuryuptake capacity by 50%. Without wishing to be bound by theory, it isbelieved that the increased selenium concentration results in asignificant decrease in the water uptake capacity of the sponge. Theseresults indicate that 3% of selenium in the PU sponge is sufficient toinduce extremely fast adsorption of mercury while maintaining highuptake capacity.

pH Stability and selectivity. The implementation of new mercury sorbentsto real-world samples such as surface waters, rain water and industrialwastewater requires from the sorbent to be stable in different pHconditions and selective against interfering compounds. The effect of pHon the capture of mercury ions (10 ppm) was investigated over a pH rangeof 1-12. As showed in FIG. 36, the sponge exhibits optimum performanceover the entire pH range. Mercury uptake capacity slightly drops from100% (undetectable levels) to 99.9% at a pH below 1 or higher than 8.This slight variation is likely caused by the ionic strength and doesnot seem to have any correlation with Hg²⁺ chemical form in solution.

To evaluate the selectivity of the NanoSe sponge and the effect ofinterfering ions, the content of tap water and lake water was analyzedin terms of 20 different chemical elements before and after exposure tothe PU and NanoSe sponge for 60 minutes (FIG. 37). The results show thatboth sponges did not retain any of the water nutrients including N, P,S, K⁺, Mg²⁺, Na⁺ and Ca²⁺, that are important when treating drinking orsurface waters. Only three other transition metal pollutants, namely Zn,Cu, and Ni, showed a significant decrease by respectively 78%, 81% and90% when using the NanoSe sponge. Moreover, the mercury removal capacityof the NanoSe sponge was not affected by the presence of these threeelements even at extremely low mercury concentrations.

To further demonstrate the applicability of the NanoSe sponge formercury sequestration in real samples, tap and lake waters spiked with 5ppm and 12 ppt mercury were analyzed. Given the ultralow concentrationof mercury analyzed, sample collection, storage and analysis followedultraclean protocol according to the US Environmental Protection Agency(US-EPA) Method 1669. Both samples showed no detectable mercury aftertreatment with the NanoSe sponge. The results demonstrate not only theability to clean environmental samples with no pretreatment, but alsothe ability to capture extremely low concentrations of aqueous mercury,which opens up new avenues in cleaning rain and surface waters.

Cytotoxicity and anti-microbial properties. Antimicrobial properties ofselenium are well known and documented. These properties can be ofimportance when the NanoSe sponge is used in aqueous or humidenvironments, where biofouling can reduce sponge performance. To assessthe antimicrobial activity of the NanoSe sponge, cytotoxicityexperiments were performed by either exposing a microbial plate growthto the sponge or immersing the sponge in the microbial growth solution.As showed in FIG. 38a , the NanoSe sponge exhibits strong antifungalproperties against Aspergillus niger (mold), Candida guilliermondii(yeast) and antibacterial properties against lactobacillus. The growthof E. coli seems to be less affected by the NanoSe sponge.

The potential use of the sponge to clean surface waters requires thesponge to be biocompatible and have minimum effect on aquatic life. TheNanoSe sponge toxicity could be caused by a potential release ofselenium. This risk was studied by exposing the sponge to mammaliancells. The sponge was incubated with cell culture media for 24 hours to72 hours, then different dilutions of the contaminated media wereprepared and their effect on mammalian cell growth measured. Thediagrams in FIG. 38b show that the sponge has no effect on cellviability when the released selenium concentrations are below 1 mg·L⁻¹.A decrease in cell viability becomes noticeable at seleniumconcentrations of 1.5 mg·L⁻¹ after exposure of the cell for 72 hours.These results highlight the importance of washing the sponge after theNanoSe is grown on the material and before the sponge is exposed tomercury. FIG. 39 shows that the sponge can be easily washed to drop theselenium released by the sponge to values below 0.14 mg·L⁻, far below atoxic concentration.

In addition to the evaluation of the biocompatibility of the NanoSesponge, the toxicity of the mercury-loaded sponge and, specifically, ofthe Se—Hg complex was investigated. One of the proven routes of mercurypoisoning is the irreversible interaction of mercury with biogeneicselenium-dependent enzymes such as thioredoxin reductase and glutathioneperoxidase. FIG. 38c shows different levels of enzyme activity ofglutathione peroxidase following an exposure to a PU sponge and to aNanoSe sponge before and after complexation with mercury. The resultsshow that the enzyme activity can be totally inhibited when the enzymeis exposed to selenium nanoparticles (SeNPs) or NanoSe sponge. A PUsponge seems to slow down the reaction but the enzyme remains active.However, when the enzyme is exposed to a NanoSe sponge that was alreadyused to capture 10 ppm of mercury, the enzyme exhibited a remarkable3-fold increase in activity as compared to the normal enzyme reaction.This unexpected result suggests that not only the complexed Se—Hgpresent in the sponge is not toxic but that the presence of the spongemay improve the enzyme reaction conditions.

Sorbent Regeneration, Leaching and disposal. Potential issues for newlydeveloped sorbents include their suitability for regeneration ordisposal—potentially significant factors in determining the final costof the technology and meeting regulatory requirements. Table 5 showsthat that the NanoSe sponge releases only from 0% to 6% of the adsorbedmercury (10 ppm) when exposed to harsh chemical treatmentsconventionally used for sorbent regeneration from mercury, including theuse of thiourea, and sodium hydroxide or 12 M hydrochloric acid. Theseresults along with those obtained with the leaching experimentsdescribed below suggest the irreversibility of the mercury capture bythe NanoSe sponge.

TABLE 5 Starting concen- Treatment tration of Hg Released Hg 12M HCl for12 hrs on 10 ppm 0.529 ppm NanoSe sponge 12M HCl for 12 hrs 10 ppm 0.653ppm on PU sponge 0.25M thiourea, 1M HCl 10 ppm 0 for 1 hr on nSe spongeNaOH (pH 12) 10 ppm 0.00426 ppm

To evaluate the non-hazardous nature of the mercury sponge after use,and the suitability for waste disposal, the leaching risk of the spongewaste was assessed using the EPA established protocols. Mercury andselenium extraction from waste sponges were performed using both theToxicity Characteristic Leaching Procedure (TCLP), used to simulatesanitary landfill conditions, and the Synthetic Precipitation LeachingProcedure (SPLP), used to evaluate the leaching potential ofland-disposed wastes under acid rainfall. Table 6 shows that a spongeloaded with 10 ppm mercury released only 2±0.2 ppb mercury with bothTCLP and SPLP, far below the EPA regulatory limits for waste disposal(Maximum Concentration of Contaminants for Toxicity Characteristic) of200 ppb. Since the same sponge was loaded with 5±0.5 mg selenium, theleaching experiment was also performed on selenium. Table 6 show arelease of 0.5 ppm, below the EPA limit of 1 ppm. Similar results wereobtained for the PU sponge without selenium, indicating that the NanoSesponge is non-hazardous and can be disposed by landfilling.

TABLE 6 Starting Starting concen- EPA limits concen- tration of fortration Selenium Released Released environment Treatment of Hg (mg) HgSelenium release TCLP on 10 ppm 5.45 2.29 ppb Hg 200 ppb NanoSe Se 1 ppmsponge TCLP on 10 ppm NA 7.95 ppb NA Hg 200 ppb PU sponge Se 1 ppm SPLPon 10 ppm 4.28 1.80 ppb Hg 200 ppb NanoSe Se 1 ppm sponge SPLP on 10 ppmNA 7.13 ppb NA Hg 200 ppb PU sponge Se 1 ppm

Materials and Methods

All chemicals including selenous acid (98%), sucrose (>99.5%),hydroquinone (99%), tryptic soy broth, tryptic soy agar, yeast mold (YM)broth, YM agar, glutathione peroxidase, nicotinamide adeninedinucleotide phosphate (NADPH), glutathione, sodium azide, hydrogenperoxide, glutathione reductase, buffers were purchased from SigmaAldrich (St. Louis, Mo., USA). Polyurethane sponges were die cut fromhigh density upholstery foam (FOAMTOUCH). All aqueous solutions wereprepared in nanopure water. The mercury analyses were done using anatomic absorption spectrometer (ThermoFischer Scientific iCE 3300, LOD0.2 ppb). Mercury samples were also sent to the University of MinnesotaResearch Analytical Lab and analyzed using a cold vapor atomicadsorption on a Tekran 2600 (Tekran Instruments Corporation, limit ofdetection: 0.2 ppt). All mercury analyses referred to in this report aretotal mercury analyses. Finally, cytotoxicity experiments were performedat the University of Minnesota Institute for Therapeutics Discovery andDevelopment.

Characterization of polyurethane sponge. The polyurethane sponge wascharacterized using scanning electron microscopy coupled with energydispersive x-ray analysis (EDXA) (JEOL 6500, 6700 SEM), Fouriertransform infrared spectroscopy (Nicollet Series II Magna IR-SystemFTIR) and Raman scattering using a Alpha300R confocal Raman microscope(WITec Instruments Corp., Knoxville, Tenn.) and DV401 CCD detector(using a wavelength of 514 nm). Average surface roughness andmicroscopic contact angle were measured using a KLA-Tencor P-7 and anMCA-3 (Kyowa Interface Science Co., Japan), respectively. Absorptioncapacity was estimated via water uptake in sponges of uniform size.

Synthesis of Selenium nanoparticles on polyurethane sponge. Thepolyurethane sponge was first soaked in 25% sucrose in nanopure waterfor 15 minutes. The sponge was then submerged in a selenous acidsolution (1.4 M) for 30 minutes. After removal of the sponge theremaining solution was stored at room temperature and used later in thesynthesis process. The soaked sponge was then carefully removed withoutsqueezing and left in an oven at 100° C. (Model SGO1E, Shel Lab,Cornelius, Oreg.) for 2 minutes. After this brief incubation, the spongewas added to a hydroquinone solution (2.2 M) for 5 minutes. Theremaining selenous acid from the previous step was added to the spongeafter exposure to hydroquinone at 65° C. The sponge was then quenched inan ice bath for 1 hour and washed with nanopure water to remove excesssolution.

Cytotoxicity experiment. Supplemented fibroblast growth medium-2 (FGM-2)media (500 mL, Lonza, Walkersville, Md.) was incubated with ananoselenium (nSe or NanoSe) sponge, a PU sponge without particles(control sponge), and free selenium nanoparticles (SeNP) alone at 4° C.Each culture was performed in duplicate making a total of 9 mediapreparations including a control consisting of plain medium. Aliquots(10 mL) were removed from each of the 9 media preps at 12 hours, 24hours, 36 hours and 48 hours and frozen at −20° C. until use. Normaladult human dermal fibroblasts (Lonza) were cultured in supplementedFGM-2 media according to supplier's instructions in T-75 flasks at 37°C., 5% CO₂. The adherent cells were trypsinized (0.25%) free and washedwith FGM-2 medium. Cells (5×10³) were plated into each well (0.1 mLtotal volume) of a 96-well plate and returned to 37° C., 5% CO₂ for 24hours. After 24 hours, the culture medium was removed from each well andreplaced with 0.1 mL of fresh FGM-2. Aliquots from the 9 media prepstaken at 48 hours were thawed and then added to appropriate wells (0.2mL total volume) to final dilutions of 1/2 (0.5), 1/4 (0.25), 1/8(0.125) and 1/16 (0.083). The plate was then returned to 37° C., 5% CO₂,for an additional 24 hours. After the additional 24 hours, 0.015 mL3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) dye(CELLTITER 96 Non-Radioactive Cell Proliferation Assay, Promega,Madison, Wis.) was added to each well and the plate was incubated at 37°C., 5% CO₂. After 1 hour, 0.1 mL stop solution was added to each welland the plate was returned to 37° C., 5% CO₂ for an additional 1 hour.The plate was then read in a Molecular Dynamics SpectraMax multi-modespectrophotometer at 538 nm.

Absorbance units read by the SpectraMax correlate with the number ofviable cells present. MTT is reduced by NADPH-dependent oxidoreductaseenzymes largely in the cytosolic compartment of the cells and results inthe formation of formazan (purple precipitate). Therefore, reduction ofMTT and other tetrazolium dyes depends on the cellular metabolicactivity due to NADPH flux.

Effect of Contact Time-Adsorption kinetics. An adsorption kineticsexperiment was conducted in order to estimate the time required to reachthe steady state for the efficient removal of Hg by the nSe sponge. Theconcentration of Hg used in the experiment was 10 ppm (10 mg/L). Contacttimes between the sponge and the solution of 1, 5, 30, 60, 180, 300,900, 1800 and 3600 seconds were used in this experiment.

Antimicrobial Experiment. The antimicrobial experiments were conductedfollowing the ASTM D2020 protocol. Briefly, spores were harvested fromone yeast species (Candida guilliermondii) and one mold (Aspergillusniger) and ˜10⁴ spores were plated on separate potato dextrose agar(PDA) plates. Next, 0.5 cm-thick disks were cut from both the nSe andcontrol sponge and autoclaved. Under aseptic conditions the discs weretransferred to the plates and incubated at the ideal conditions for eachspecies. Specifically, for Candida guilliermondii the plates wereincubated at 25° C. for 3 days and for Aspergillus niger the plates wereincubated for 5 days at 24° C. Similarly, gram negative bacteria (E.coli spp) and gram positive bacteria (Lactobacillus spp) were diluted toa concentration of 10⁵ cells and spread on tryptic soy agar (TSA) platesand MRS agar plates respectively. Again, 0.5 cm disks were taken fromthe nSe sponge and were transferred to the plates. The plates were thenincubated at 37° C. for 24 hours (E. coli spp) and 72 hours(Lactobacillus spp).

Effect of pH of Hg Adsorption. The effect of pH on Hg adsorption by thenSe sponge was studied. For the experiment a 10 ppm (10 mg/L) Hgsolution was prepared from a stock solution of 1000 mg/L (AAHG-1,Inorganic Ventures, Christiansburg, Va.). The pH was adjusted using anAccumet AB150 pH meter in a range from 1-8, 10, and 12. Serial dilutionsof 50 mL were used to ensure minimal error while preparing dilutions.After preparation of the mercury solution, the pH was adjusted withsodium hydroxide and hydrochloric acid. Sponges were treated in asimilar manner described above in the adsorption kinetics experimentwith a contact time of 1 minute.

Adsorption isotherm. To study the adsorption behavior of Hg on theadsorbent, a range of concentrations of Hg (1 mg/L to 50 mg/L) was used.The Langmuir adsorption isotherm model was used to fit the experimentaldata of Hg²⁺ sorption onto nSe sponge. The mercury solutions were againprepared from the stock solution and the pH was adjusted to 6. Then, 75mg of the nSe or control sponge was put in a vial with 10 mL of themercury solution. The vials were placed in a rotator (Thermo ScientificTube Revolver) and mixed for 18 hours at 40 rpm. The samples were thenanalyzed for mercury as described above.

Selectivity. To study the uptake behavior of Hg of the adsorbent in thepresence of other interfering elements, a selectivity experiment wasperformed. Copper, nickel and zinc are known to be adsorbed by theselenium. Both nSe and control sponges were treated with 10 ppm ofCuCl₂, Ni(SO₃)₂ and Zn(SO₃)₂ separately following a similar proceduredescribe above with a contact time of 5 minutes. Next, sponges weretreated a combination of these salts and 10 ppm Hg to assess competitiveelement capture (5 minutes contact time).

Application on real samples (lake and tap waters). To test theefficiency of the nSe sponge on real world samples, lake water sampleswere taken from Como Lake (St. Paul, Minn., USA) following the UnitedStates Environmental Protection Agency (EPA) Method 1669. For thesampling, 40 mL VOA EPA certified vials were used. The samples werepreserved with 6M HCl prior to analysis. After collection, lake waterand tap water samples were spiked with 12 ppt and 5 ppm of Hg. Thespiked solutions were treated with nSe sponge and control sponge with acontact time of 1 minute. The samples were then measured for trace Hg.

Toxicity of the Se—Hg complex: enzyme activity experiment. The samplesponge was treated with Hg. The activity of glutathione peroxidase (GPx)was analyzed according to the protocol of Esworthy et al., CurrentProtocols in Toxicology. Wiley, USA. 7.1.1-7.1.32; 1999. Thus, 100 μL of50 U/mL GPx were mixed with 630 μL sodium phosphate buffer (50 mM, pH7.0), 100 uL glutathione (GSH) (10 mM), 100 μL NADPH (2 mM), 10 μLsodium azide (1.125 mM), and 10 μL of glutathione reductase (GR) (100U/mL). The well-mixed enzyme solution was then added to the sponge for atotal contact time of 2 minutes. Upon liquid sample collection, 50 μL of5 mM H₂O₂ was added as the substrate. The decrease in NADPH was measuredusing a UV spectrophotometer (Shimadzu UV-1800) at 340 nm for 7.5minutes and was used to study GPx activity. Control experiments includeuntreated nSe sponges and polyurethane sponges without Se or Hg. Theenzyme assay was also tested against a free Hg solution (10 ppm) and aswell as free selenium nanoparticles (SeNP).

Leaching Experiment. To model the effect of Hg treated sponges inmunicipal waste systems, EPA methods 1311 and 1312 were used. Method1311, the Toxicity Characteristic Leaching Protocol (TCLP), models theleaching behavior of a particular waste material. Briefly, Hg treatedsponges were cut into small pieces with a diameter less the 1 mm andplaced in an extraction fluid consisting of glacial acetic acid andsodium hydroxide (pH 4.93). This solution was rotated end over end on arotator (Thermo Scientific Tube Revolver) at 30 rpm for 18 hours. Next,method 1312, the Synthetic Precipitation Leaching Procedure (SPLP),models leaching characteristics of a waste material in the naturalenvironment. Again, Hg treated sponges were cut into small pieces, addedto an extraction fluid (60/40 weight percent sulfuric and nitric acidswith pH 4.20) and then rotated for 18 hours at 30 rpm. After the 18 hourtreatment, all extract solutions were separated from the sponge pieces,acidified to a pH<2 with nitric acid and analyzed for Hg.

Mercury Regeneration. In order to assess the recyclability and/orreusability of the sponges, Hg treated sponges were treated with avariety of regeneration agents. Control and Hg treated sponges (10 ppm)were treated for 1 hour in a glass beaker with a 10 mL mixture of 0.25 Mthiourea and 1 M hydrochloric acid. Additionally, regeneration wasassessed under acidic (10 mL 12 M HCl) and basic conditions (10 mL NaOH,pH 12).

Example 7

To use the methods described herein for mercury capture in flue gas suchas emissions from coal-fired plants, selenium nanomaterials were grownon activated carbon (AC) pellets and AC scrubbers/filters.

Briefly, AC pellets or an AC filter (the material) was first soaked in25% sucrose in nanopure water for 15 minutes. The material was thensubmerged in a selenous acid solution (1.4 M) for 25 minutes. Afterremoval of the material the remaining solution was stored at roomtemperature and used later in the synthesis process. The soaked materialwas then carefully removed and dried in a vacuum oven (−2.6 kPa) at 110°C. (Isotemp vacuum oven Model 280A, Thermo Fisher, Scientific, Waltham,Mass.) for 10 min. After drying, the material was added to ahydroquinone solution (0.7 M) for 10 minutes at 65° C. The remainingselenous acid from the previous step was added to the material afterexposure to hydroquinone. The material was then washed with nanopurewater.

The SEM images of FIG. 40 show the successful growth of seleniumnanospheres and nanofilms on these two supports (AC pellets and ACfilters). The images were obtained after thorough washing of thematerials showing that the selenium nanomaterials are strongly attachedto the supports. The images in FIG. 40B1 and FIG. 40B2 show that theselenium nanomaterials also grow inside the bulk material of the ACpellet.

The complete disclosure of all patents, patent applications, andpublications, and electronically available material (e.g., GenBank aminoacid and nucleotide sequence submissions; and protein data bank (pdb)submissions) cited herein are incorporated by reference. The foregoingdetailed description and examples have been given for clarity ofunderstanding only. No unnecessary limitations are to be understoodtherefrom. The invention is not limited to the exact details shown anddescribed, for variations obvious to one skilled in the art will beincluded within the invention defined by the claims.

What is claimed is:
 1. A method of preparing a selenium nanomaterialcomprising: forming a saccharide coating on a surface of a solid supportmaterial, treating the solid support material having the saccharidecoating on the surface with a selenous acid solution, and heating thesolid support material to form the selenium nanomaterial on the surfaceof the solid porous support material.
 2. The method of claim 1 whereinthe saccharide comprises a monosaccharide, a disaccharide, or apolysaccharide, or a combination thereof.
 3. The method of claim 1wherein the saccharide comprises sucrose, or fructose, or a combinationthereof.
 4. The method of claim 1 wherein the saccharide containsfructose.
 5. The method of claim 4 wherein the saccharide comprisesfructose, sucrose, lactulose or turanose.
 6. The method of claim 1wherein the saccharide coating comprises a homogeneous saccharidecoating.
 7. The method of claim 1 wherein forming a saccharide coatingon a surface of a solid support material comprises soaking the solidsupport material in a saccharide solution.
 8. The method of claim 7further comprising removing excess saccharide solution from the materialafter soaking the solid support material in the saccharide solution. 9.The method of claim 1 wherein the selenium nanomaterial on the surfaceof the solid support material has an average size of 50 nm to 150 nm.10. The method of claim 8 wherein heating the solid support materialcomprises heating at a temperature in a range of 110° C. to 120° C. 11.The method of claim 11 further comprising quenching or washing the solidsupport material having selenium nanomaterial on the surface.
 12. Amethod of preparing a selenium nanomaterial comprising: soaking a solidsupport material in a saccharide solution to form a homogeneoussaccharide coating on a surface of a solid support material, treatingthe solid support material having the saccharide coating on the surfacewith a selenous acid solution, and heating the solid support material toform homogeneous selenium nanomaterial on the surface of the solidporous support material.
 13. The method of claim 12 wherein the pH ofthe selenous acid solution is less than
 3. 14. The method of claim 12wherein the pH of the selenous acid solution is less than 1.6.
 15. Themethod of claim 12 wherein the saccharide comprises a monosaccharide, adisaccharide, or a polysaccharide, or a combination thereof.
 16. Themethod of claim 12 wherein the saccharide comprises sucrose, orfructose, or a combination thereof.
 17. The method of claim 12 whereinthe selenium nanomaterials have a diameter from 10 nm to 1000 nm.
 18. Anarticle comprising a solid material having a selenium nanomaterial boundto a surface thereof, the article made by the process comprising:forming a saccharide coating on a surface of a solid support material,treating the solid support material having the saccharide coating on thesurface with a selenous acid solution, and heating the solid supportmaterial to form the selenium nanomaterial on the surface of the solidporous support material.
 19. The article of claim 17 wherein the articlecomprises less than 5% saccharide.
 20. The article of claim 17 whereinthe support material comprises activated carbon, a sponge, a film, afabric, a non-woven material, or a metal-organic framework (MOF), or acombination thereof.